Copycat Costco Vanilla Cake

Name: Copycat Costco Vanilla Cake
Prep time: 50 min
Cook time: 26 min
Yield: 8-10
Ingredients: 4 Egg whites, large; 1 Egg yolk, large; 1 tbsp Baking powder; 1 Copycat costco vanilla mousse; 2 tbsp Cornstarch; 1 5/8 cups Granulated sugar; 4 cups Powdered sugar; 1 1/4 tsp Salt, fine; 1 Sprinkles; 2 tbsp Vanilla; 1/2 cup Vegetable shortening; 1 3/4 cup Butter, unsalted very soft; 1 cup Buttermilk; 3 tbsp Whole milk or heavy cream; 2 tbsp Water; 2 1/2 Plus 2 tablespoons cake flour