Preheat the oven to 180°C. Grease and line with parchment paper the bottom of a 20 cm cake pan then grease and flour the whole pan.
The batter will be divided into two portions so if you have two 20 cm cake pans you can bake them at the same time, if not, bake the first half and then use the same pan for the second one.
In a bowl mix egg whites, 60 ml buttermilk and vanilla extract until combined.
In another bowl mix together flour, baking powder and, sugar for 20 seconds.
Add in the remaining buttermilk and butter. Mix on low speed until the dry ingredients are moistened then increase to high speed and mix for 1 1/2 minutes to aerate and develop the cake’s structure.
Make sure to scrape down the sides of the bowl once in a while. Add the egg mixture in 3 batches mixing well after each addition (about 20 seconds). Then put in all of the sprinkles and mix gently by hand to distribute them, with just 3-4 moves.
Divide the batter into two prepared cake pans, smooth the surface and bake for about 30 minutes. Check if the cake is baked – insert a toothpick or a knife in the center and if it comes out clean it’s done, if not, bake it for a few more minutes and check again.
Cool the cakes on a wire rack.