Instructions

• Step 1: Prepare Your Pans - Preheat your oven to 350°F (175°C). Grease your two 9-inch round cake pans with butter or non-stick spray and dust with a little cake flour to prevent sticking.
• Step 2: Mix the Dry Ingredients - In a medium bowl, whisk together the cake flour, baking powder, and salt. Set this mixture aside while you prepare the wet ingredients.
• Step 3: Cream the Butter and Sugar - In a large bowl, with an electric mixer, beat the unsalted butter and granulated sugar together until light and fluffy (about 3-4 minutes).
• Step 4: Add the Wet Ingredients - Add the egg whites, whole milk, and vanilla extract to the butter and sugar mixture. Beat until combined, scraping down the sides of the bowl as needed.
• Step 5: Combine Wet and Dry Ingredients - Gradually add the dry ingredients to the wet ingredients, mixing just until combined. Gently fold in the rainbow jimmies.
• Step 6: Bake the Cakes - Divide the batter evenly between the prepared cake pans. Bake for 25-30 minutes or until a toothpick comes out clean. Let cool for 10 minutes, then invert onto a cooling rack.
• Step 7: Make the Frosting - In a large bowl, beat the unsalted butter until creamy. Gradually add the sifted confectioners' sugar, mixing on low speed. Add salt, vanilla extract, and milk or cream to reach desired consistency.
• Step 8: Frost the Cake - Once the cake layers are cool, place one on a serving plate, spread frosting on top, add the second layer, and frost the top and sides. Decorate with sprinkles.