01 -
Preheat oven to 350°F/180°C, then butter and line three 6-inch pans with parchment on the bottom.
02 -
In a large container, whisk together the egg whites, whole egg, vanilla extract, and milk. Leave it for now.
03 -
Use the paddle attachment on your electric mixer at a low speed. Combine the dry ingredients and mix for about a minute before adding the cold butter. Keep mixing until you get a crumbly texture.
04 -
Pour the wet mix into the dry ingredients in two portions. Scrape the sides and bottom in between and after adding. Mix until fluffy and light.
05 -
Evenly pour the batter into the pans you prepped. Bake for 25-35 minutes, checking with a tester in the center—few crumbs should stick.
06 -
Cool the cakes in their pans on racks for about 20 minutes before pulling them out.
07 -
Cut uneven tops off the cake layers. Stack with frosting between each layer. Cover the cake with a thin layer of frosting, chill for 30 minutes, then finish with a top coat. Add sprinkles for flair.