step 1
Preheat oven to 350 degrees F (180 degrees C). Line three 8-inch round pans with parchment rounds, and grease with Non-Stick Baking Spray (as needed).
step 2
Mix together All-Purpose Flour (3 1/4 cups), Baking Powder (1 Tbsp), Granulated Sugar (3 cups), and Salt (1 tsp) in a stand mixer with a paddle until fully combined.
step 3
Mix chunks of Unsalted Butter (1 cup) slowly into the dry mix, at a low speed. Continue to mix until no large chunks of butter remain, and the mixture becomes crumbly.
step 4
Pour in Pasteurized Egg White (1 cup), and mix on low until just incorporated. Mix in the Buttermilk (1 1/2 cups) in two installments, at a low speed.
step 5
Add in Vanilla Extract (1/2 Tbsp), Almond Extract (1/2 Tbsp), and Vegetable Oil (2 Tbsp) and mix at a low speed until fully incorporated. Scrape down the sides of the bowl with a spatula, then beat on low speed for about 15 seconds (the key is to mix until the ingredients are just incorporated so that the batter isn't over-mixed).
step 6
Fold the Sprinkles (3/4 cup) into the cake batter using a rubber spatula, just they've evenly distributed.
step 7
Divide batter evenly between the prepared cake pans. Bake for 34-36 minutes, or until a toothpick comes out clean.
step 8
Allow the pans to cool for 10 minutes, then run an offset spatula around the perimeter of the pan to separate the cake from the pan. Place cake layers into the freezer for 45 minutes, to accelerate the cooling process.
step 9
While the cake layers bake and cool, make the Vanilla Buttercream Frosting. Beat Unsalted Butter (3 cups) on medium speed with a paddle attachment, until smooth.
step 10
Slowly add in the Powdered Confectioners Sugar (12 cups), 1 cup at a time. Alternate with small splashes of Heavy Cream (1/3 cup).
step 11
Once fully mixed, add in the Vanilla Extract (1 1/2 Tbsp) and Salt (1 tsp), and beat on low until the ingredients are fully incorporated, and the desired consistency is reached. If the frosting is too thick, add in additional cream (1 tsp at a time). If the frosting is too thin, add in more powdered sugar (¼ cup at a time).
step 12
To assemble, stack, and frost cake layers on a greaseproof cake board, using a dab of frosting to help stick the first cake layer to the board. Add an even layer of buttercream between each cake layer as well as a spoonful of the rainbow sprinkles.
step 13
Apply a thin coat of frosting around the cake, to fully cover the cake layers. Smooth using a bench scraper then chill the cake in the fridge (10 minutes) or freezer (5 minutes) until the frosting is firm to the touch.
step 14
Add a second, thicker layer of frosting to the cake, and smooth using a bench scraper.
step 15
Divide the remaining frosting between six bowls, and color a variety of different colors. Fit the piping bags with a variety of tips we used Wilton 1M and 4B frosting tips.
step 16
Pipe a variety of textures and shapes around the cake, fully covering it. To achieve this underwater look we used ruffles, rosettes, and stars.
