Preheat waffle iron to 400°F.
Whisk together flour, baking powder, sugar and salt in a medium mixing bowl.
In a separate mixing bowl, beat egg whites with a mixer on high speed until stiff peaks form.
Add egg yolks, milk, butter, and vanilla extract to dry ingredients (combined in step 2); gently fold in whipped egg whites.
Drop by large spoonfuls onto waffle iron until most of the wells are covered; close the lid; cook for ~4 minutes, or until golden brown (if your waffle iron has an indicator light, your waffles are likely ready when light indicates).
Remove waffle(s) from iron with a fork; serve or keep warm on a plate in a 250°F oven; proceed with remaining batter.
