Instructions

CAKE

1. Adjust a rack to the center position in the oven and heat to 350 degrees. Spray 3 8-inch round cake pans with non-stick baking spray and set aside. In a food processor, process the rainbow sprinkles until coarsely ground, about 8 to 10 pulses. Set aside until needed.
2. In a medium sized bowl, whisk together the milk, egg whites and vanilla.
3. Attach the paddle attachment to a stand mixer. On low speed combine flour, sugar, baking powder and salt. Add butter one piece at a time. Continue to combine until the butter is the size of peas, about 1 minute. Reserve ½ cup of the milk mixture, and pour remaining into the dry ingredients. Increase speed to medium-high and beat until light and fluffy, about 1 minute. Reduce the mixer speed to medium-low and add the reserved milk mixture to the batter and beat until combined, about 30 seconds (the batter may look curdled at this point). Give the batter a final stir by hand and stir in ground rainbow sprinkles.
4. Divide the batter evenly among the prepared cake pans and smooth the tops with an offset cake spatula or rubber spatula. Bake for about 20 to 25 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs attached, rotating pans halfway through baking. Let cakes cool in their pans for 10 minutes on wire racks. Invert cakes onto the wire racks to cool completely, about 2 hours.

SOAKING SYRUP

1. Add water and sugar in a small saucepan and cook over medium heat, stirring occasionally until sugar has dissolved. Turn off the heat and stir in extract and flavored vodka if using.

BUTTERCREAM

1. Pour egg whites and sugar in the bowl of a stand mixer, and whisk them together by hand to combine. Create a double boiler by filling a saucepan with a few inches of water and placing the bowl on top. The bottom of the bowl should not touch the water. Heat saucepan over medium heat.
2. Attach a candy thermometer to the bowl and heat the egg white mixture to 160 degrees, whisking often. Once the mixture reaches 160 degrees, about 10 to 12 minutes. Carefully transfer the bowl to the stand mixer.
3. With the whisk attachment attached, beat the egg white mixture on high speed for about 8 to 10 minutes until egg whites hold medium-stiff peaks. The mixer bowl should be room temperature with no residual heat coming from the top of the bowl.
4. Remove the whisk attachment from the mixer and replace it with the paddle attachment. With the mixer on low speed, add the butter a tablespoon at a time, then add the vanilla extract and vodka if using. Once the butter is combined increase the mixer speed to medium-high and beat until the buttercream is smooth and silky, about 5 minutes. Add in rainbow sprinkles and gently stir in by hand.

ASSEMBLE

1. Trim off cake domes that may have formed during baking on each cake layer, creating a flat and even surface. Poke a few holes on the top of the cake layer with a wooden skewer. With a pastry brush, brush on soaking syrup (about 3 tablespoons for each cake layer). With an offset cake spatula, spread about ¾ cup buttercream on top of the first cake layer, leaving about ½-inch from the edge free of buttercream. Repeat this process with the remaining cake layers. Top the last cake layer with a generous amount of frosting, smoothing to the edges and down the sides, removing excess frosting as you go. Enjoy!