Clean the cake ring and place it in the center of a sheet pan lined with clean parchment or a Silpat. Use 1 strip of acetate to line the inside of the cake ring.
Put the two half circle scraps in the ring, like so:
And fill the remaining gap between the two with the remaining cake scraps:
You're going to have more cake scraps than can fit in the gap. Simply take the excess cake scraps and press them down into the cake layer, using the back of your hand to achieve a flat and even layer:
Okay, maybe not, but close enough.
Next, dunk a pastry brush in the birthday cake soak and give the layer of cake a good, healthy bath of half the soak:
Use the back of a spoon to spread one-fifth of the frosting in an even layer over the cake:
Sprinkle one-third of the birthday crumbs evenly over the top of the frosting. Use the back of your hand to anchor them in place:
Use the back of a spoon to spread a second fifth of the frosting as evenly as possible over the crumbs:
Next, set one of your cake rounds on top of the frosting. If one of your cake rounds is jankier than the other, use it here for the middle and save the prettier round for the top layer. Repeat the process above.
When it's completed, nestle the remaining cake round into the frosting. By this point, you should have a fairly tall cake:
With those famous Milk Bar layers:
Cover the top of the cake with the final fifth of the frosting. Garnish the frosting with remaining birthday crumbs:
Transfer the cake and the sheet pan that it's on to the freezer and freeze for a minimum of 12 hours to set the cake and filling.
At least 3 hours before you are ready to serve the cake, pull the sheet pan out of the freezer, and, using your fingers and thumbs, pop the cake out of the cake ring:
This was actually more difficult than I anticipated. The cake/acetate sheets were stuck around the cake ring pretty hard, so I ended up taking a knife and running it between the acetate sheet and the cake ring, and then pushing the cake base up and letting the cake ring slide down my arm. Sorry I don't have visuals of this, I couldn't really take photos of the process as I had my hands full.
Gently peel off the acetate:
And transfer the cake to a platter or cake stand. Let it defrost in the fridge for a minimum of 3 hours before serving.
And now, enjoy!