Preheat oven to 350 degrees. Spray three 8 or 6-inch cake pans with baking spray and line the bottom with parchment paper.
In a large bowl mix the 2 ¾ cup cake flour, 1 tbsp baking powder, and ¾ tsp salt.
Combine 1 cup buttermilk and 2 tsp vanilla in a bowl
In a standing mixer with a paddle attachment, cream the butter and sugar for 5 minutes. The butter should be very pale, light, and fluffy.
Alternate adding the dry ingredients and wet ingredients, starting and ending with the dry ingredients. So, you’ll add the mixes for flour, milk, flour, milk, flour. Mix each until barely combined. You do not want to overmix.
In a separate bowl (or using the same bowl cleaned very well), whisk the 5 egg whites to stiff peaks.
Gently fold ⅓ the egg whites into the batter. Once combined, fold in the remaining egg whites.
If adding sprinkles, mix together 1 tbsp flour and ⅓ sprinkles. Then, gently fold into the batter.
Pour the batter evenly into the prepared cake pans. Tap on the counter to spread it evenly and release any air bubbles.
Bake at 350 degrees for 26-35 minutes, depending on the size of the pan you use. You’ll know it’s done when you can insert a toothpick and it comes out clean and it gently springs back when you touch it.
Let cool in the pan for 20 minutes then transfer to a wire rack to finish cooling.
Make sure the cakes are completely cool before starting to frost.