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Wellesley Fudge Cake

yield: 1 double layer, 8-inch square cake
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Ingredients

For the Chocolate Cake

  • 2 1/2 cups (12.5 ounces) all-purpose flour
  • 2 teaspoons baking soda
  • 1 teaspoon baking powder
  • 1/2 teaspoon kosher salt
  • 3/4 cup (6 ounces) hot water
  • 1/2 cup (1.5 ounces) unsweetened natural cocoa powder
  • 1 cup (8 ounces) unsalted butter, at room temperature
  • 2 cups (14 ounces) granulated sugar
  • 2 large eggs
  • 1 cup (8 ounces) buttermilk, at room temperature
  • 2 teaspoons pure vanilla extract

For the Chocolate Fudge Frosting

  • 1 1/2 cups "tightly packed" (10.5 ounces) dark brown sugar
  • 1 cup (8 ounces) evaporated milk, divided into two 1/2 cup portions
  • 1/2 cup (4 ounces) unsalted butter, at room temperature, divided into two 4 tablespoon portions
  • 1/2 teaspoon kosher salt
  • 8 ounces dark (at least 60% cacao) chocolate, roughly chopped
  • 1 teaspoon pure vanilla extract
  • 3 cups (12 ounces) confectioners' sugar, sifted

Instructions

For the Chocolate Cake

  • Center a rack in the oven and preheat to 350 (F). Grease two 8-inch square cake pans, line with parchment paper, grease parchment, and flour pans. Whisk 2 1/2 cups all-purpose flour, 2 teaspoons baking soda, 1 teaspoon baking powder, and 1/2 teaspoon kosher salt together in a medium bowl. Whisk 3/4 cup hot water and 1/2 cup unsweetened natural cocoa powder in a small bowl until smooth; set aside. Using a freestanding electric mixer fitted with a paddle attachment, beat 1 cup unsalted butter and 2 cups granulated sugar on medium-high speed until pale and fluffy, about 3 minutes. Add 2 large eggs, one at a time, and beat until combined. Reduce speed to low and add flour mixture in 3 additions, alternating with 1 cup buttermilk in 2 additions, scraping down the bowl as needed. Slowly add the cocoa mixture and 2 teaspoons pure vanilla extract and mix until incorporated. Use a rubber spatula to scrape down the paddle and sides of the bowl and mix any residual ingredients into the batter by hand.
  • Divide batter evenly between prepared pans and smooth tops with a rubber spatula. Bake until a toothpick inserted into the center of each cake comes out with few crumbs attached, 35 to 40 minutes. Let cakes cool in pans on a wire rack for 15 minutes. Remove cakes from pans, discarding parchment, and let cool completely on rack before frosting.

For the Chocolate Fudge Frosting

  • Heat 1 1/2 cups brown sugar, 1/2 cup evaporated milk, 4 tablespoons unsalted butter, and salt in a large saucepan over medium heat until small bubbles appear around perimeter of the pan, around 4 to 8 minutes. Reduce heat to low and simmer, stirring occasionally, until large bubbles form and the mixture has thickened and turned deep golden brown, about 6 minutes; transfer to a large bowl. Stir in remaining 1/2 cup evaporated milk and remaining 4 tablespoons unsalted butter until mixture is slightly cool. Add 8 ounces chocolate and 1 teaspoon vanilla extract and stir until smooth. Whisk in 3 cups confectioners' sugar until incorporated. Let cool for 15 to 20 minutes, stirring occasionally.
  • Line edges of the cake platter of your choice with 4 strips of parchment paper to keep the platter clean. Place 1 cake layer on the platter. Spread 1 cup frosting evenly over the top of the cake, right to the edge of the cake. Top with second cake layer, pressing lightly to adhere, then spread remaining frosting evenly over the top and sides of the cake. Refrigerate the cake until frosting is set, about 1 hour. Carefully remove parchment strips before serving.