1) Preheat waffle iron
2) Whisk together flour, baking powder, salt and sugar (all the dry ingredients) in a large mixing bowl.
3) In a separate small mixing bowl whisk together egg yolks, milk, vanilla extract, and butter.
4) Make a well in the center of the dry ingredients and pour the liquid ingredients into it. Stir just enough to combine and get a moist mixture (do not over-mix)
5) Beat the egg whites until stiff, but not dry.
6) Gently fold the egg whites into the batter.
7) Pour or ladle the batter into the waffle iron and bake as directed by your iron.