Ingredients

The following ingredients have 12 Servings
  • 1 1/2 cups cake flour
  • 1 1/4 cups granulated sugar
  • 1 1/2 teaspoons baking powder
  • 1/2 teaspoon salt
  • 3/4 cup (1 1/2 sticks) unsalted butter, softened and cut into cubes
  • 1/2 cup plus 2 tablespoons buttermilk, divided
  • 2 large eggs
  • 1 large egg yolk
  • 1 teaspoons vanilla extract
  • 1/2 cup confetti quin sprinkles
  • 3/4 cup (1 1/2 sticks) unsalted butter, room temperature
  • 2/3 cup dark or Dutch processed cocoa powder, sifted
  • 2 to 2 1/2 cups powdered sugar
  • 1/4 to 1/2 cup heavy cream, more or less as needed
  • 3/4 teaspoon vanilla extract
  • 1/4 teaspoon fine sea salt

Instruction

  • Preheat oven to 350 degrees F. Butter the bottoms and sides of a quarter sheet pan (or equivalent). Line bottom with parchment paper; butter parchment.In a large mixing bowl or the bowl of a stand mixer, combine flour, sugar, baking powder, and salt. Mix to combine. Add butter and 1/2 cup of buttermilk. Mix on low speed until flour is evenly moistened, then increase speed to medium-high and beat until light and fluffy, 1 to 2 minutes, scraping down the sides of the bowl as needed.In a small bowl, beat remaining 2 tablespoons buttermilk with eggs, egg yolk, and vanilla. Add to the batter mixture one-third at a time, mixing well after each addition. Stir in sprinkles. Spread batter into prepared pan(s).Bake for 20 to 25 minutes, rotating halfway through baking, until edges are lightly golden brown and the center bounces back when you gently press it with your finger. Transfer to a wire cooling rack to cool completely, about 1 hour. Run a knife or thin spatula around the edge of the pan, then invert the cake onto wire rack. It should come out easily and cleanly. Remove parchment from the bottom. At this point the cake can be wrapped tightly in a double layer of plastic wrap and frozen until ready to use (in fact, I recommend you freeze the cakes overnight, as the frozen cakes will be easier to level and frost later).To prepare frosting, in a large mixing bowl, beat butter on medium-high speed until smooth and fluffy, 2 to 3 minutes. Add cocoa powder and beat until smooth. Add powdered sugar, 1/2 cup at a time, mixing well after each addition. As frosting thickens, add a few tablespoons of cream as needed. Depending on the temperature and consistency of your frosting, continue alternating additions of cream and powdered sugar, until frosting is light and fluffy. The amount of cream you need will vary depending mainly on the room temperature; on a cold day in February I used about 1/2 cup of cream, but on a hot day I might not need any at all. Use your best judgement here. Add vanilla and salt and beat on high for an additional 1 to 2 minutes or until light and fluffy.To assemble, cut cake in half using a large serrated knife. Place one layer, flat side down, on a cake stand or serving platter. Spread on about 1 cup of frosting onto cake using an offset spatula. Position second layer on top and press to adhere.Position your number template on top of the cake, and trim off excess. For round areas, cut off one triangle at a time until you have an overall rounded shape. For the center hole, I used a round cookie cutter to cut out the top layer, then a small serrated or pairing knife to gently cut out the lower layer. Use a small spoon to scoop it out.Cover the entire cake with a thin layer of frosting. This “crumb coat” will keep the stray crumbs in place and make frosting the cake easier. Refrigerate for about 15 minutes to allow this crumb coat to set, then spread with remaining frosting. Decorate with additional confetti sprinkles, if desired.