Name: Rainbow Unicorn Cake Recipe
Prep time: 10 min
Cook time: 150 min
Total time: 180 min
Ingredients: 1 box Pillsbury Funfetti Cake Mix; 1 ¼ cup (10 ounces or 283 grams) water, at room temperature; ½ cup (4 ounces or 113 grams) neutral (like canola, grapeseed, vegetable) oil; 4 large egg whites, at room temperature; yellow food coloring; orange food coloring; red food coloring; 1 box Pillsbury Funfetti Cake Mix; 1 ¼ cups (10 ounces or 283 grams) water, at room temperature; ½ cup (4 ounces or 113 grams) neutral (like canola, grapeseed, vegetable) oil; 4 large egg whites, at room temperature; blue food coloring; purple food coloring; green food coloring; 2 cups (16 ounces or 454 grams) unsalted butter, at room temperature; 2 teaspoons pure vanilla extract; pinch of kosher salt; 4 cups (16 ounces or 454 grams) confectioners' sugar, sifted; 1 to 2 teaspoons whole milk (see baker's notes); 2 cups (16 ounces or 454 grams) unsalted butter, at room temperature; 2 teaspoons pure vanilla extract; pinch of kosher salt; 4 cups (16 ounces or 454 grams) confectioners' sugar, sifted; 1 to 2 teaspoons whole milk (see baker's notes); blue food coloring; red (or pink) food coloring; purple food coloring

Rainbow Unicorn Cake

Rainbow unicorn cakes are popular cake designs for children’s birthday parties, baby showers, and more. According to Google, the trend was first started by Canadian bakery, Jenna Rae Cakes (whose first book is coming out in October—I’m so excited for it that I even contributed a blurb for their backcover!). But hold the phone… what exactly is a unicorn cake, any way? These are layer cakes that are decorated to look like unicorns, complete with a unicorn horn and a colorful mane made out of buttercream frosting. It’s pretty epic… however, my recipe takes it next level. Why? My unicorn cake is a rainbow unicorn cake. When sliced, it reveals six different colored layers of funfetti cake! Each layer is dyed a different color to match the different colors of the rainbow: red, orange, yellow, green, blue, and violet.

How to Make an Easy Rainbow Unicorn Cake

Okay, you read all of that and thought that it all sounded like a lot of work. And I’m not going to lie: baking and decorating six different colored layer cakes is “A Commitment”. Making this cake definitely took the majority of my day.

So, I decided to take shortcuts where I could. Instead of making the cake from scratch, I decided to use one of my favorite cake mixes: Pillsbury Funfetti. This boxed mix makes a super moist white cake studded with colorful rainbow sprinkles. Truth be told, I have a soft spot in my heart for funfetti cake from a box mix. In my cookbook, Weeknight Baking, I wrote about how I first fell in love with baking by making funfetti box mix in my college dorm kitchen.

And it turns out I’m not the only one with a soft spot for funfetti. Most people already prefer the flavor of funfetti cake made from a box than a funfetti cake made from scratch. You can see an example of this on my friend Erika’s blog, The Pancake Princess. Erika tested and ranked some of the internet’s favorite funfetti cake recipes from scratch against Pillsbury Funfetti box mix. The box mix cake came out close to the top!

How to Make Box Cake Mix Better

Additionally, there are ways to improve boxed cake mix. Right now, there’s a popular TikTok video where a professional baker advocates using cake mix. However, instead of following the instructions on the box (which typically instruct you to make the cake mix with 3 egg whites, water, and oil), she ups the number of eggs in the batter and uses milk and butter instead of water and oil. Folks who have tried it claims this hack results in “elevated” and “luxurious” cupcakes.

Truthfully, I wasn’t brave enough to try that hack for this unicorn rainbow cake recipe. I mean…funfetti cake mix already makes good cake—why mess with it, ya know?!). But I do have my own ways to make box cake mix better. My number one trick? Pair the cake with a homemade frosting from scratch! For this unicorn rainbow cake recipe, I made a classic, vanilla buttercream frosting from my friend Lyndsay’s book, Coco Cake Land. If you’re not following her blog or her Instagram already, be sure to check it out. She makes some of the cutest cakes!

Anyway, in her book, Lyndsay specifically talks about how she devleoped her classic American buttercream frosting to be “less” sweet than traditional buttercream frostings. As a result, she uses an equal ratio of butter and confectioners’ sugar in the frosting recipe (most buttercream frostings have a 1:2 ratio of butter to sugar). Because funfetti cake is already pretty sweet, I thought that it would work well in this cake. I was right! It worked wonderfully in this unicorn rainbow cake recipe.

Why You Should Make This Rainbow Unicorn Cake Recipe

In addition to looking pretty and cute, here are all the reasons why you should make this rainbow unicorn cake:

This rainbow unicorn cake recipe is super precise and in-depth.

Whenever I develop recipes for this blog, I spend a lot of time researching recipes from cookbooks, food magazines, and other blogs for inspiration—you can learn more about my recipe development process in this blog post. However, many of the rainbow cake recipes and unicorn cake tutorials I saw lacked depth. Specifically, many of them failed to discuss what kind of tools you need to make and decorate a unicorn cake. Others failed to include tips on how to divide cake evenly between cake pans. Lucky for you, I tried to cover it all this blog post so you have everything you need in one spot!

This rainbow unicorn cake recipe’s design and look can be easily customized to fit any special occasion or celebration.

Pillsbury Funfetti cake mix typically makes two 8-inch or 9-inch layer cakes. However, for this rainbow unicorn cake recipe, I divided the batter between three 8-inch cake pans to make thinner layers. Specifically, I made two boxes of cake mix and produced six layers of cake to represent the different colors of a rainbow. But if that’s not your jam, no worries! Go ahead and follow the cake mix’s instructions to make just make two (or four!) layers of cake. You can also skip dyeing each layer a different color and just make a traditional funfetti cake.

And speaking of color, I went with traditional “unicorn colors” to make the unicorn cake’s fringe. Specifically, I used a pale blue, pale pink, and lavender color. However, I’ve also seen different colored rainbow cakes on Pinterest—I especially like these red and yellow Harry Potter unicorn cakes, and this glamorous all-black-everything unicorn cake. So although my instructions below instruct you on how to make a fairly standard unicorn cake, feel free to use your imagination and come up with your own color schemes and designs!

Different parts of this rainbow unicorn cake recipe can be made ahead to fit your schedule.

I’m not going to lie—most layer cake recipes take all day to make. First, you make the cakes and wait for them to cool completely before assembling and decorating. Next, you make the frosting and assemble the cake. If you’re using a complicated frosting like Swiss meringue buttercream, it can take up to a full half hour to make the frosting! Decorating the cake can be time-consuming, too. Fancy cake designs (like this Christmas wreath cake, this fault line cake, and this geode cake) can take hours to put together.

Luckily, this recipe is pretty forgiving and flexible. The cake can be made ahead far ahead of serving. Simply freeze the layers until you’re ready to assemble the cake. Be sure to check out more of my notes on how to make this cake fit into your schedule (and, spoiler alert: if you’re into this kind of time management, definitely check out my cookbook). And Lyndsay’s buttercream frosting takes just 5 minutes to make. Cool, right?

And despite the fancy look of the unicorn cake’s buttercream fringe and mane, it actually doesn’t take that long to put together—I promise! With the right piping tips (which I discuss in the blog post below), all you need to do is pipe little dots of frosting. In no time at all (okay, maybe 10 to 15 minutes worth of work), you’ll have an adorable unicorn mane!

Tools You Need to Make A Rainbow Unicorn Cake

Now that I’ve convinced you to make this rainbow unicorn cake, let’s talk about the tools you need to make it!

**Here’s everything you need to make the rainbow unicorn cake layers:**

featured:
kitchen scale || food coloring set || cake pans

A Digital Kitchen Scale

This rainbow unicorn cake recipe instructs you to use a digital scale to divide the cake batter into different bowls.

Why do I need a digital scale for this recipe? I thought we were using cake mix.

Ahh, yes. One of the benefits to using cake mix is that you don’t need to measure out any dry ingredients—it’s all been done and mixed together to make the cake mix. However, we’re not using the cake mix to make the cake itself. Instead, we’re using the scale to make sure that we have even cake layers.

What does that mean? For even cake layers, I like to actually weigh out the layers with the digital scale to make sure they’re even. The easiest way to do this is to set a prepared cake pan on a digital scale and tare it to “0”. Pour batter into the pan until the scale registers the weight listed in the recipe (because yes, I’ve included the approximate weight of the batter needed for each pan!). Repeat with the second and third cake pans. I know it sounds like a pain, but this is how professional bakers get such even layers on their cakes—I promise.

However, for this recipe, instead of pouring the batter into the pans first, I instruct you to pour it into three different bowls instead. You then add a different color of food coloring into each bowl and mix it into the batter to create the different colored layers of the rainbow unicorn cake.

Okay, you’ve convinced me. What’s the best digital scale?

A good scale will cost less than $30 and offer readings in a variety of measurements like ounces, grams, and milliliters. I personally recommend the Primo Digital Kitchen Scale by Escali. I’ve had mine for many years now, and it shows no sign of stopping anytime soon. That being said, if you’re looking for more options, both The Kitchn and The Wirecutter (though both agree with me that my recommendation is best!) have great round-ups of different digital kitchen scales.

Hm, I don’t think I’m convinced. Do I really need to measure out the layers for this rainbow unicorn cake recipe?

No, you don’t really need a digital scale. In a pinch, you can just divide the layers by eyeballing them. But I guarantee you that your layers will all come out different sizes and heights this way.

Another alternative is to divide the batter with a liquid measuring cup. However, this method is messy and requires more equipment that you then need to clean up. Based on the weight measures, I think that each cake pan will need around 1 ⅓ cups of batter per pan. Specifically, divide the batter by pouring 1 ⅓ cups of batter into three bowls, and then dye them with food coloring (see below). However, because I haven’t done this method myself, I cannot guarantee the accuracy of these volume measures. Please leave a comment in the section below if you tried this method!

Food Coloring

This rainbow unicorn cake recipe instructs you to dye the different bowls of cake batter with different colors of food coloring to match a rainbow.

The Best Food Coloring Set to Make a Rainbow Cake

The most commonly available food coloring set in grocery stores is this small McCormick set. It comes with only four colors: red, yellow, green, and blue. While it works in a pinch (see below), I recommend upgrading to a larger food coloring set with more colors to match that of a rainbow. Officially, a rainbow has seven colors: red, orange, yellow, green, blue, indigo, and violet. So to make your life easier, you want a food coloring kit that also includes an orange and a purple dye.

Food Coloring Kit Recommendations

This AmeriColor Student Kit gel food coloring kit comes with all the colors you need for a rainbow, plus a few extra pastels (which are perfect for the unicorn cake’s buttercream mane!) and solids like black and brown. I personally have the professional AmeriColor “Nifty-Fifty” kit that comes with 50 colors. Although it’s a little on the spendy side, I cannot say enough good things about my set. However, if you’re on a budget, I also recommend this Wilton 8-Count Gel Icing Color Set. It also comes with all the colors you need for the rainbow cake layers, as well as a pastel pink that would be perfect for the unicorn cake’s buttercream mane.

Liquid Food Coloring Versus Gel Food Coloring

Note that, while the McCormick food coloring is liquid-based, both the AmeriColor and Wilton food coloring kits I recommended are gel-based. What does that mean, exactly? McCormick’s food coloring is water-based. According to this Kitchn article, water-based dyes are less intense and weaker than gel-based food colorings. You’ll likely need to use a lot of food coloring to achieve a brighter or deeper color.

Alternatively, gel-based food coloring is made with a combination of water, glycerine, and/or corn syrup. This combination makes its consistency more gel-like and its food coloring abilities more concentrated. Gel-based food colorings are much more effective in dying a large amount of batter, producing dark, saturated colors with smaller amounts of dye. That makes them perfect in this rainbow unicorn cake!

Can I make this rainbow unicorn cake recipe with a standard food coloring set of just four colors?

In a pinch, yes, you can make this rainbow unicorn cake recipe with the McCormick food coloring set. However, you’ll likely need to mix multiple colors in the same bowl to create the missing colors. Check out the guide below:

To make an orange-colored cake layer, mix 1 to 2 drops of red food coloring into a bowl of batter that’s already been dyed yellow. It’s important to add the darker dye to a light-colored cake batter. It’s much harder to dye a dark-colored batter a lighter color!

To make a purple (violet)-colored cake layer, add 2 drops of red food coloring and 1 drop of blue food coloring to an undyed bowl of cake batter. Both red and blue food coloring can be equal in their intensity. To make a purple color, it’s best to mix both in at the same time and use a 2:1 ratio of red to blue.

Note that, in addition to making the orange and purple colors to make the rainbow cake layers, you also need to make batches of pastel frosting to make the unicorn cake’s mane. To make pastel pink (or blue) frosting, add 1 drop of red (or blue) to a big bowl of white buttercream frosting. Keep mixing until you have a homogenous, pastel color.

Do I even need to use food coloring for this rainbow unicorn cake?

No, not really. I mentioned earlier that you can just make this a standard unicorn funfetti cake. Follow the instructions to bake 2 boxes of funfetti cake mix into 4 cake layers. That’s it! However, note that you still need food coloring for the unicorn cake’s buttercream mane.

Three 8-inch Round Cake Pans

This rainbow unicorn cake instructs you to bake two boxes of Pillsbury Funfetti cake mix in three 8-inch round cake pans.

What are the best cake pans to use?

TL/DR: Light-colored, metal baking pans with straight sides, preferably all from the same brand. Specifically, I recommend the pans from Williams-Sonoma’s Goldtouch® Nonstick line.

For baking, always choose a light-colored pan over a dark one. Dark colors absorb heat more quickly. Doing so causes the bottom and sides of baked goods to bake much faster than their centers. Some bakers swear by their glass pans, but I exclusively recommend pans made of metal. Metal conducts heat more efficiently and cools quickly when done. Glass pans stay warm for a long time, continuing to cook your food long after it’s been pulled out of the oven, leading to overdone baked goods.

Finally, it’s also important to use cake pans with straight sides, as opposed to slanted sides. Although they take up much more space in your cupboard (since they’re unstackable), they produce straight-sided cakes that are much easier to layer and frost. If you’re just starting your own collection of cake pans, I recommend pans from Williams-Sonoma’s Goldtouch® Nonstick line, which fit all of the parameters I just described. For this rainbow unicorn cake, I used three of these 8-inch round cake pans.

Can I use 9-inch cake pans instead?

Yes, with reservations. Bake Time will likely decrease since the batter will be spread out wider. I recommend checking for doneness 5 to 10 minutes earlier than the time listed in the recipe. Your cake layers will also be thinner than mine.

**And finally, here’s everything you need to decorate the rainbow unicorn cake:**

featured:
cake boards || rotating cake stand || offset spatula
unicorn cake topper || piping bag and tips set

A 9-inch or 10-inch Cake Board

This rainbow unicorn cake recipe instructs you to assemble the cake layers on a 9-inch cake board.

What’s a cake board?

A cake board is a stiff piece of cardboard that’s placed underneath the cake. The cake board makes it easy to transfer the cake from the rotating cake stand (which we’ll get to in a hot second) and onto a different serving plate or cake stand.

Cake boards come in different sizes to match the most commonly used cake pans. Professionals like to match the size of their cake board to their cake pan—that is, professional bakers will place an 8-inch round cake on top of an 8-inch round cake board. You can see this in action in this Vietnamese iced coffee cake recipe, this Nutella fault line cake, and this geode cake.

That being said, it’s easier for beginners and novice bakers to use a slightly larger cake board (e.g. pairing an 8-inch round cake with a 9-inch round cake board). Doing so makes it easier to pick the cake up for transfer. In fact, I recommend using a slightly larger cake board for this unicorn cake recipe. That way, you can pipe some of the fringe onto the board to make it look like the unicorn mane is cascading down the cake stand!

Do I really need a cake board for this rainbow unicorn cake recipe?

No, you don’t really need a cake board. This recipe instructs you to place the cake on a cake board, and then place the whole thing in the center of a rotating cake stand (which, we’ll get to shortly). However, you can place the cake on its serving plate instead (and then place the serving plate on the rotating cake stand). If you’re opting for this method, it’s best to use a plate that’s completely flat—like any of these plates from Crate and Barrel’s Mercer collection (which I love and have, BTW). A flat plate gives you a level surface that makes it easier to frost the cake evenly and smoothly.

A Rotating Cake Stand/Turntable

This rainbow unicorn cake recipe instructs you to frost the cake layers on a 9-inch cake board.

What’s a rotating cake stand?

A rotating cake stand, or a cake turntable, is a cake stand with a plate that rotates 360 degrees. This function allows bakers to smooth the sides of cakes evenly and efficiently. The best cake stands are sturdy, with a heavy base that doesn’t easily move when accidentally nudged. I found my rotating cake stand at a local restaurant professional supply store; however, this Ateco model is very similar. If you’re on a budget, opt for this cheaper, lightweight plastic version by Wilton. I also like this rotating cake stand from Food52. It looks like a regular cake stand, so there’s no need to put yourself through the scary task of moving your beautiful, finished cake onto a serving platter!

Can I make this rainbow unicorn cake without a rotating cake stand?

Yes, but I don’t recommend it. In a pinch, you can use a lazy Susan by setting the cake on a serving platter, then placing it on an upside-down bowl on the lazy Susan’s center. You’ll be able to rotate the cake this way. That being said, it’s likely that you’re going to have a much harder time frosting smooth sides on your cake.

An Offset Spatula

This rainbow unicorn cake recipe instructs you to frost the cake layers with an offset spatula.

What’s an offset spatula?

While spatulas for cooking have a wide rectangular or square head, offset spatulas have a thin, blunt blade. This blade enables you to easily spread and scrape sauces, fillings, frostings and more when baking. If you don’t already own one, I recommend investing in both a short and long offset spatula with sturdy metal blades. These ones from Ateco are my favorites since their wood handles are photogenic. However, this dishwasher-friendly version with plastic handles is likely the better choice for non-professional food bloggers. For this rainbow unicorn cake, I recommend using a long offset spatula (like this one that is almost 10 inches!) to help you frost the cake’s tall sides.

Can I make this rainbow unicorn cake without an offset spatula?

Yes, but your life will be infinitely easier if you invest in an offset spatula. But without one, you can use a baking spatula, a butter knife, or the back of a spoon to cover the cake completely in frosting. Then, use a bench scraper or a (clean) ruler to smooth the sides of the cake.

Unicorn Cake Topper Accessories: A Horn, Ears, and Eyes

This rainbow unicorn cake recipe instructs you to decorate the cake with cake toppers like a unicorn horn, ears, and eyes.

Where can I buy a unicorn cake topper?

Amazon! Amazon has a wide selection of inexpensive-yet-really-cute unicorn cake toppers available. I personally went with this unicorn cake topper kit. I liked that it was fairly minimalist; some kits already come with flowers and decorations. It also came with everything: a unicorn horn, ears, AND eyes. Some kits only come with a horn and ears.

Wait, are those eyes edible?

Hahaha, no. The unicorn eyes that came in my kit are made out of stiff cardboard. We peeled them off before eating the cake.

Can I make my own unicorn cake topper instead?

Yes! This YouTube tutorial from The Bearfoot Baker shows you how to make a unicorn horn, ears, and eyes with fondant. I’ve also seen other home bakers dye a small amount of frosting black and pipe on the eyes with a piping bag fitted with a small round tip.

Piping Bags and Piping Tips

This rainbow unicorn cake recipe instructs you to use piping bags with different piping tips to frost the unicorn cake’s buttercream frosting mane.

The Piping Tips I Used For This Rainbow Unicorn Cake

For this unicorn cake, I used the following piping tips:

Ateco #825. This piping tip is an open star piping tip. Mine came in this Ateco jumbo piping tip set. I piped the pastel blue dollops in the unicorn cake’s buttercream mane with this tip.
Ateco #847. Ateco #847 is a closed star piping tip. Similarly, mine came from this Ateco jumbo piping tip set. I piped the lavender-colored dollops in the unicorn cake’s buttercream mane with this tip.
Wilton #30. Wilton #30 is another closed star piping tip. However, it is much smaller in size and stature than Ateco #847, leading to dramatically different shapes and dollops. I piped the peach-colored dollops in the unicorn cake’s buttercream mane with this tip.

Note that you do not need to use the exact same piping tips I did. You can use whatever piping tips you have on hand, though I recommend using at least one closed star piping tip and another open star piping tip for variety. You can see different piping tip options in Wilton’s Decorating Tips chart. This chart shows you the different results between round tips, open star tips, closed star tips, multi-opening tips, and more!

The Best Piping Bag and Tip Set for Beginners

You can buy individual piping tips, but it adds up pretty quickly—each tip typically clocks in at between $4 to $7. So if you don’t own any piping tips, I definitely recommend investing in a starter piping bag and tip kit like this $16 one from Wilton. Wilton’s kit comes with an assortment of 18 different round, open and closed star tips. It also comes with an offset spatula and a handful of disposable piping bags (note that I used three different piping bags to frost the buttercream mane). That’s almost everything you need to make this rainbow unicorn cake!

How to Make a Rainbow Unicorn Cake

To make a rainbow unicorn cake, we start by making the different colored funfetti cake layers. Here are the basic steps to make all the cake layers for a rainbow unicorn cake:

First, make the rainbow cake layers:

Prep your ingredients for the funfetti cake mix. (Prep Time: <5 minutes)
Okay, most cake mixes don’t actually require that much prep beyond opening the box. But Pillsbury Funfetti cake mix gives you the option of using 3 large whole eggs or 4 large egg whites to use in its mix. This unicorn rainbow cake recipe works best with the egg white variation. It makes a really good white cake batter that’s easy to dye and makes the colors pop! This prep time accounts for separating the eggs.
Make the cake batter. (Work Time: 5 minutes)
I make the cake mix by mixing together the liquid ingredients—the egg whites, oil, and water—in a large bowl, then mixing in the cake mix.
Divide the cake batter and dye it different colors. (Work Time: 10 minutes)
Use the digital scale to divide the cake batter evenly between three bowls. Add a drop of food coloring in each and use a rubber spatula to mix in the dye until homogenous and fully saturated.
Bake the cake layers. (Bake Time: 18 minutes)
Pour the dyed batter into three prepared cake pans and bake for 18 minutes. Pillsbury Funfetti cake mix actually instructs you to bake for longer (34 to 38 minutes for 8-inch round cake pans, 29 to 33 minutes for 9-inch round cake pans). But because we’re dividing the batter into THREE pans, we end up making much thinner layers that require a shorter Bake Time in the oven.

Note that you’ll be going through the process I just described TWICE. To make a rainbow unicorn cake, we need to bake TWO boxes of funfetti cake mix. The first box of cake mix makes the red, orange, and yellow cake layers. The second box of cake mix makes the green, blue, and violet layers.

How to Make Icing for a Rainbow Unicorn Cake

After the rainbow cake layers are baked and cooled to room temperature, make the frosting! This rainbow unicorn cake uses a basic, American buttercream frosting from scratch.

Next, make the buttercream frosting:

Prep your ingredients for the buttercream frosting. (Prep Time: 5 minutes)
When making frosting, it’s especially important to make sure that your butter is at room temperature and that the confectioners’ sugar is sifted. Cold butter and unsifted confectioners’ sugar makes lumpy frosting that is difficult to frost and riddled with bumps!
Make the buttercream frosting. (Work Time: 5 minutes)
After you’ve prepped your ingredients, making the buttercream frosting is an easy process. Simply beat the butter until creamy, then gradually add the confectioners’ sugar and a splash of vanilla. Easy, right?

Similar to the cake making process, you’ll actually need to make the buttercream frosting twice. Make the first batch of buttercream frosting once the cakes have cooled completely and you’re ready to assemble and crumb coat the cake (more on that in a second). Once the cake is crumb coated, place it in the refrigerator and chill for at least 30 minutes. Towards the end of this chill time (around 20 minutes in), make the second batch of buttercream frosting to finish assembling and decorating the cake.

How to Decorate a Rainbow Unicorn Cake

The most time-consuming part of this unicorn cake recipe is actually assembling and decorating the cake itself.

First, start by assembling the rainbow unicorn cake:

Assemble the cake layers. (Work Time: 15 minutes)
Place the violet cake layer on a cake board (or a serving plate) in the middle of the rotating cake stand. Take an offset spatula and drop about ½ cup of the frosting right in the middle of the top of the cake. Spread it evenly all over the top, just like you would spread butter on toast. Place the blue cake layer on top of this frosting, stacking it evenly on top of the violet cake. Repeat the process I just described with the remaining green, yellow, orange, and red layers (yes, in that order!).
Crumb coat the cake. (Work Time: 30 minutes)
A crumb coat is a thin layer of frosting that’s spread over the naked cake to trap crumbs. If you’ve ever tried to frost a cake without a crumb coat, you’ll know that crumbs can shake loose from the cake and get caught in the frosting, leaving your cake with unsightly bumps. The crumb coat seals in any crumbs, allowing you to apply thicker and smoother layers of frosting later.

To apply a crumb coat, follow the instructions to stack the cakes, layering frosting between each cake to “glue” them together. Then cover the surface of the entire layer cake with a thin layer of frosting—this is the crumb coat! Use just enough frosting to cover the entire cake completely. Refrigerate for 30 minutes, just enough for the frosting to harden.

If you have no idea what I’m talking about, check out this tutorial on the Wilton YouTube channel for a visual representation:

Then, finish frosting the rainbow unicorn cake:

Once the crumb coat is close to set, make the second batch of buttercream frosting. (Work Time: 5 minutes)
Remember I told you that you’d need to make TWO batches of buttercream frosting? About 20 minutes into the crumb coated cake’s chill time, make the second batch of buttercream frosting to prep yourself for finishing the unicorn rainbow cake.
Cover and smooth the cake completely with the buttercream frosting. (Work Time: 30 to 60 minutes)
Use the offset spatula to spread the frosting all over the top and sides of the cake evenly. Once the cake is completely covered, hold the length of the offset spatula’s blade against the frosting as you rotate the cake stand. Doing so will smoothen out the frosting. Check out the video tutorial below from my friend Tessa from Style Sweet on how to do so (she also has an awesome blog post with more details). Although she uses a cake comb/scraper in her video, her technique also works with an offset spatula:

Finally, decorate the rainbow unicorn cake:

Divide the remaining frosting between three bowls and dye each bowl with a different color of pastel food coloring. (Work Time: 10 minutes)
Unlike when measuring cake layers, there’s no need to be precise here. I eyeballed dividing the frosting into three bowls. To dye the frosting, add 1 to 2 drops of food coloring to each bowl. Then, use a small rubber spatula to mix the dye into the frosting until completely homogenous and saturated.
Transfer each dyed buttercream into its own piping bag with its own tip. (Work Time: 5 minutes)
Wilton also has a great video tutorial on how to fill piping bags with buttercream frosting. If you’re a beginner, I recommend only filling each bag with a small amount of frosting. It makes it easier to control the bag and pipe cleaner designs!
Arrange the unicorn cake toppers on top of the cake. (Work Time: 5 minutes)
Arrange the unicorn horn and ears on top of the cake. The unicorn set I recommended comes with little plastic sticks that hold the accessories in place. You can cover these plastic bases with piped frosting.
Pipe the buttercream frosting mane on the unicorn cake. (Work Time: 20 minutes)
Now comes the fun part! Use the different piping bags to pipe little dollops of frosting on top of the cake and down one side of the cake in a cascading fashion. Don’t forget to keep one side of the cake completely free of frosting—this is the the unicorn cake’s face! Carefully place the unicorn eye stickers on the side of the cake with no frosting to create a unicorn face.

**Make it Weeknight Baking: How to Make This Rainbow Unicorn Cake Fit Into Your Schedule**

Whenever I bake an elaborately decorated cake like this rainbow unicorn cake, I break down the recipe to make its different components over multiple days. Why? It can be really time-consuming to make the cake all in one day! First, you need to bake the cakes and wait for them to cool completely. Then you need to make the frosting, assemble the layers, frost a crumb coat, and wait for it to set. After that, you need to finish decorating the whole thing! You can see how this recipe is turning into a full day’s worth of work (as well as sitting around and waiting for things to cool and set) in the kitchen.

To make sure I’m not stuck in the kitchen all day, I stretched the work for this unicorn rainbow cake recipe over a few days. Here’s what I did:

Day 1: Make the First Set of Rainbow Layer Cakes (Total Time: around 35 minutes, including Bake Time)

Follow the recipe instructions for making, dyeing, and baking the first three layers of the funfetti cake layers. Once cool, tightly wrap each layer in its own sheet of plastic wrap and freeze. In general, cakes freeze really well. Frozen cakes are easier to frost, and once thawed, the cakes are perfectly moist and flavorful. However, don’t refrigerate unfrosted cakes! It dries them out and makes them go stale faster. If you don’t have room in your freezer, it’s better to wrap the cakes and leave them on the counter overnight.

Day 2: Make the Second Set of Rainbow Layer Cakes (Total Time: around 35 minutes, including Bake Time)

Similar to Day 1, follow the recipe instructions for making, dyeing, and baking the first three layers of the funfetti cake layers. Once cool, tightly wrap each layer in its own sheet of plastic wrap and freeze.

Day 3: Make the First Batch of Frosting, Assemble the Layers and Crumb Coat the Cake (Total Time: around 55 minutes)

Follow the recipe instructions for assembling the layers and making a crumb coat for the cake. Refrigerate the cake overnight to set the crumb coat.

Day 4: Make the Second Batch of Frosting, Finish Frosting the Cake, and Serve (Total Time: around 60 minutes)

Follow the recipe instructions for frosting the cake completely and piping the unicorn cake’s buttercream frosting mane.

That being said, if four days to make one cake sounds like too long to wait, there are other ways you can shorten the timeline and make it fit your schedule! You can make all the cakes in one day, or crumb coat and completely frost the cake in one day, too.

Also—if you are into this sort of time management baking, definitely check out my cookbook, Weeknight Baking. I break down cake and pie recipes this way so that you could ostensibly make an elaborate recipe over the course of a few weeknights.

Unicorn Rainbow Cake Recipe Troubleshooting and FAQ

FAQ: Unicorn Rainbow Cake Ingredients

Where can I buy Pillsbury Funfetti cake mix?

Pillsbury Funfetti cake mix is available in the baking aisle of most major grocery stores and convenience stores like Target and Walmart in the United States. In a pinch, you can also buy it online through Amazon. Just know that doing so comes at a premium—a box of Funfetti cake mix usually costs between $1 to $3 at a grocery store.

Can I use other cake mix instead?

Yes! Be sure to check out my baker’s notes below (in the yellow box) on how to adjust this recipe and make it with another kind of boxed cake mix.

Can I make the funfetti cake from scratch instead?

Absolutely. I recommend this princess bakery funfetti cake recipe and this chocolate-frosted funfetti cake recipe on Hummingbird High. Both are adapted by a recipe from my friend, Molly Yeh. She is the funfetti cake queen!

FAQ: Unicorn Rainbow Cake Recipe Results

Why does your rainbow unicorn cake only have six layers? Doesn’t a rainbow have SEVEN colors?

Bahahah, I was waiting for somebody to ask this question. Because yes, technically a rainbow has seven colors: red, orange, yellow, green, blue, indigo, and violet. One of my original plans for this recipe was to grab two boxes of funfetti, make them all in one bowl, and divide the whole thing between seven cake pans to make a 7-layer cake.

But then I started researching “rainbow” cakes on both Pinterest and Instagram and noticed that a LOT of them just had six layers. Many skipped indigo and just featured a violet layer after the blue layer. Later, when I was reading the Wikipedia page for rainbows (yes, this is the sort of thing I do in my spare time apparently), I learned that the inclusion of indigo as its own color in the rainbow is actually controversial! Specifically:

“It is customary to list indigo as a color lying between blue and violet, but it has never seemed to me that indigo is worth the dignity of being considered a separate color. To my eyes it seems merely deep blue.”
– Isaac Asimov

Whoa there, Isaac. Those are some harsh words!

While I’m not 100% sure I agree with Isaac and his harsh stance on the harmless color, I decided to forgo the indigo layer. I wanted to make the rainbow unicorn cake recipe as easy as possible for you guys! Making three layers at a time for a 6-layer cake is the best way to do that.

Can I make this rainbow unicorn cake an 8-inch (or 9-inch), 4-layer cake instead?

Yes! Pillsbury Funfetti cake mix actually gives you a ton of options to make the mix in different cake pans. If you want to make a more traditional 4-layer cake, follow their instructions to bake the cake mix in two 8-inch or 9-inch round cake pans. If you want to make a 4-layer cake, you’ll need a second box of funfetti cake mix, too. However, note that the weight of the batter in each cake pan will change.

At this point, I’m assuming that you’re NOT dyeing the cake rainbow colors and are instead planning on making a regular 4-layer funfetti cake. In my recipe below, I instruct you to measure out between 11 to 11.15 ounces (312 to 316 grams) of batter per cake pan. For a 4-layer cake, you’ll need to measure out between 16 to 16.5 ounces (454 to 468 grams) of batter instead. I also instruct you to pour the batter into different bowls; there’s no need to do that here. You can just pour and measure the batter in the cake pans.

Finally, follow the Bake Time for an 8-inch (or 9-inch) round cake pan that’s listed on the cake mix box.

Can I make this rainbow unicorn cake an 8-inch (or 9-inch), 2-layer cake instead?

Yes, absolutely! You can just buy one box of Pillsbury Funfetti cake mix and follow my instructions above for dividing the mix into two even layers and baking according to the box’s instructions. Note that you may only need to make one batch of frosting since you’ll end up with a much smaller cake.

Alternatively, you can also take the cake mix and divide it between three cake pans to make a 3-layer cake. Follow the instructions in my recipe for dividing the batter evenly between three pans and baking accordingly.

FAQ: Unicorn Rainbow Cake Storage

How to store rainbow unicorn cake

The rainbow unicorn cake can be stored at room temperature, under a cake dome or a large bowl turned upside down, for up to 1 day. After that, cover loosely the sliced parts with plastic wrap and refrigerate for up to 2 days.

Can you freeze rainbow unicorn cake?

Yes! You can freeze rainbow unicorn cake in two different ways:

Freeze the baked, unfrosted rainbow cake layers. I mentioned earlier that most baked cakes freeze really well. Once the cake layers have cooled to room temperature, tightly wrap each layer in its own sheet of plastic wrap and freeze. The cake is best within 3 months of making, but can be frozen for a full year after. Be sure to check out the section above on how to use the frozen cake layers to build this rainbow unicorn cake!

Freeze slices of the assembled rainbow unicorn cake. Similar to how couples freeze a slice of wedding cake to enjoy on their anniversary, you can do the same with this cake! Tightly wrap individual slice of rainbow unicorn cake in plastic wrap and freeze. Similar to my advice above, the cake tastes best within 3 months o making, but can be frozen for a full year. If you’re planning on storing it long term, double wrap each slice in plastic wrap AND a layer of aluminum foil. The aluminum oil prevents the frosting from absorbing any weird odors or flavors in the freezer.

To serve frozen rainbow unicorn cake, thaw overnight in the fridge, then on the counter at room temperature for 1 to 2 hours before serving.

Best Rainbow Unicorn Cake Recipe Tips

Best Technique Tips

For even cake layers, I like to divide the batter by weighing out the layers with a digital scale to make sure they’re even. The easiest way to do this is to set a prepared cake pan on a digital scale and tare it to “0”. Pour batter into the pan until the scale registers the weight listed in the recipe (because yes, I’ve included the approximate weight of the batter needed for each pan!). Repeat with the second and third cake pan.
However, if you’re using a different cake mix other than Pillsbury Funfetti cake mix, the weights listed in my recipe likely won’t work. I only provided instructions for Pillsbury Funfetti cake mix! Don’t fret, though. You can still figure out the right amounts yourself with whatever cake mix you choose. Simply weigh out the (empty) mixing bowl you’re planning to make the cake with and write its weight on a piece of paper. Keep it close! You’ll need it soon. After you’ve made your cake mix in the bowl, weigh the bowl WITH the cake mix once more. Subtract the bowl’s empty weight from this figure and divide it by 3. The resulting amount is the weight of the batter you’ll need for 3 cake pans.

Best Cake Dyeing Tips

I didn’t include exact teaspoon measures for the food coloring in this recipe. Why? The amount of food coloring you use will vary and depend on whether you went with a water-based or gel-based dye (learn more by scrolling up to the Ingredients section of this blog post). Add food coloring to the cake layers, either by squirting drops or using a ¼ teaspoon measure, and mix. Keep going until you achieve a bright, saturated color. Don’t be afraid to use more than you think you need (especially with the darker colors like red, blue, green, and purple). The cake batter’s colors tend to become less saturated after being baked. However, don’t go too overboard, either. Some food dyes can affect the taste of the cake. I wouldn’t add more than 1 teaspoon of food coloring to each layer (especially if you are using a gel-based dye).
The easiest way to dye the cake layers is to pour the batter into small bowls (I used cereal bowls) and mix with a small rubber spatula (I recommend this Norpro set) or spoon. If you want to minimize the amount of dirty dishes to clean up, I recommend using the same spatula to mix all the layers. However, this only works if you pair similar colors and start with dyeing the lighter colors. For instance—make the red, orange, and yellow layers from the same box mix. Dye the first cake layer yellow, then orange, then red. You’ll only need to use one spatula for the job! You can also almost get away with this technique for the green, blue, and violet layers. Dye the first cake layer blue, then purple. Rinse the spatula off and then dye the remaining layer green.

Best Frosting Making Tips

If the buttercream frosting is too stiff to spread or or pipe, a touch of milk (around 1 to 2 teaspoons) will help loosen it a little. I personally didn’t need to use any when I made this cake, but it was also an unseasonably warm day, lol. Again, don’t be afraid to use your judgement here!

More Epic Layer Cakes Similar to Rainbow Unicorn Cake

Simpler (Yet Equally Delicious) Layer Cakes

This post was last updated on 8/15/2020.

Cakes Layer Cakes

posted by Michelle Lopez on June 12, 2020 (last updated Aug 30, 2023)

7 comments Leave a comment »

7 comments on “Rainbow Unicorn Cake”

Yael @ Nosherium — June 12, 2020 @ 8:46 am Reply

Aaahhhhhhhh this is such a great post! You’ve outdone yourself, Michelle – beautiful cake, a dash of nostalgia, lots of information and explanation! I sure hope this is one of your birthday cakes!
Albertina Geller — June 13, 2020 @ 5:23 am Reply

The perfect cake for the month! And you have explained everything perfectly. Amazing post! Thank you for sharing 🙂
Ashley — October 18, 2020 @ 4:38 pm Reply

Super informative. First time making a themed cake for one of mY daughters and she loved it! I didn’t do the rainbow fillings, but I did use a lot of the advice you provided to help guide me…. thanks a bunch!

Rainbow Unicorn Cake