Preheat the oven to 350°F. Line muffin pans with cupcake liners.

In a bowl, combine flour, sugar, baking powder, and salt. Add butter and mix until crumbly.

In a separate bowl, mix half of the milk with vanilla extract.

In another bowl, whisk egg whites with remaining milk.

Gradually add the milk mixture to the dry ingredients and beat for 5 minutes. Add egg white mixture and beat for 1 minute.

Stir in sprinkles and fill liners 2/3 full. Bake for 17-20 minutes.

Let cool completely before frosting.