Preheat oven to 350 degrees F.
Line two 12-cup cupcake tins with paper liners and set aside.
Mix sugar and butter in a mixer until very creamy, scraping sides as needed, 1 to 2 minutes. Add the eggs and yolks, one at a time. Add the milk, water, and vanilla and blend.
In separate bowl mix flour, baking powder, and salt in a medium bowl.
Add the dry ingredients, in 3 batches to the wet mixture.
Evenly pour the batter into the prepared cups, filling them 3/4 of the way full.
Bake until the cakes are just firm and spring back when gently pressed 18 to 25 minutes.
Allow to cool.