Spray your pans with pan spray. Line the bottoms with parchment circles and spray again.
In the bowl of a stand mixer, combine flour, sugar, baking powder and salt and mix on low to combine.
In another bowl, combine egg whites, 1/4 of the milk and vanilla. Whisk lightly.
Add the butter and the other 3/4 of the milk to the dry ingredients. Mix on low to moisten, and then beat on medium for 1 1/2 minutes. Scrape down the sides of the bowl.
Add the remaining milk in 3 additions, beating for 20 seconds each time and scraping bowl as necessary.
Scrape batter into prepared pans and smooth the tops. Bake at 350 degrees, F, for 25-35 minutes or until lightly golden brown. A tester inserted in the center should come out clean, and the cake should spring back when lightly pressed in the center.
Cool in pans for 10 minutes, then turn out and reinvert to cool right-side up.