Preheat the oven to 350° and line your muffin pans with paper cups.
In a medium bowl whisk together flour, baking powder and salt.
Beat butter in a bowl with mixer fitted with the paddle attachment until pale and creamy. Slowly at sugar and continue beating until light and fluffy.
Using a glass measuring cup combine milk and vanilla.
Turn your mixer on low and add 1/3 of dry ingredients alternatively with 1/2 milk mixture, repeat, and stir just until combined.
In a clean bowl with the whisk attachment beat egg whites starting at medium speed and working up to medium high until stiff peaks form.
Using a large spatula fold in 1/3 of the egg whites into the batter, stirring slowly add the remaining egg whites try to keep the egg volume and stir until all combined.
Using a scoop fill muffin papers with approximately 3 T of batter.
Bake one pan at a time in the middle rack of your oven for 18-20 minutes until a tooth pick comes out clean.