Preheat oven to 350°F. Line and spray 2 9-inch round cake pans and set aside.
In a small bowl, whisk the flour, baking powder, baking soda, and salt together. In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and sugar together on medium-high speed for 2 minutes. Add the egg whites, milk, and almond extract, and beat for another minute. Add in the flour mixture and whisk just until combined. Gently fold in the sprinkles.
3 cups all-purpose flour, 1½ teaspoons baking powder, ¾ teaspoon baking soda, ¾ teaspoons kosher salt, 1½ cups unsalted butter, 2 cups granulated sugar, 6 egg whites, 1½ cups milk, ¾ teaspoon almond extract, 1½ cups rainbow sprinkles
Evenly divide the cake batter between the cake pans (about 977 grams each). Place into the oven to bake for 40 minutes, or until a toothpick inserted comes out clean or with moist crumbs on it. Remove from the oven and place on a cooling rack to cool.
While the cakes are cooling, make the frosting. Place all of the frosting ingredients into the bowl of a stand mixer fitted with the paddle or whisk attachment. Beat on low for 1 minute to allow the powdered sugar to incorporate. Increase the mixer speed to high and whip for 4-6 minutes. Fill a piping bag fitted with a tip with ¾ cup of frosting.
1 cup unsalted butter, 1 cup vegetable shortening, 5½ cups powdered sugar, 2-3 tablespoons heavy cream, ½ teaspoon kosher salt, ½ teaspoon pure vanilla extract, ¼ teaspoon almond extract
Once the frosting is made and the cakes are cooled, place one cake layer onto a cake stand or plate. Spread about ¾ cup of frosting onto the layer before placing the second layer of cake on top. Spread frosting onto the top of the cake. Spread a thin layer of frosting around the sides of the cake. Once the sides are frosted, a wall of frosting will have formed around the top edge of the cake. Using an offset spatula at a 45-degree angle, pull the frosting wall towards the center of the cake. Spread extra sprinkles onto the top of the cake. Pipe frosting swirls around the edge of the cake in a circle pattern.
½ cup rainbow sprinkles
Slice and serve.