Preheat a waffle iron
according to the manufacturer's instructions. Sift
the flour, baking powder, and salt into a medium bowl and set aside. In a second bowl, use a whisk to beat together the egg yolks and sugar until sugar has dissolved and eggs have turned a pale yellow. Add the milk, melted butter, and vanilla extract
and whisk to combine. Add the flour mixture to the egg-milk mixture and whisk
just until blended. Do not overmix.
In a third bowl, beat the egg whites with an electric mixer
until soft peaks form, about 1 minute. Using a rubber spatula
, gently fold the egg whites into the waffle batter. Don't overmix! Coat the waffle iron with nonstick cooking spray, if required, and pour enough batter
in the iron to just cover waffle grid.
Close and cook as per manufacturer's instructions until golden brown, about 2 to 3 minutes. In checking for doneness, open the waffle iron carefully and watch out for steam. Do not open the waffle iron, though, for at least 1 minute. Repeat cooking with remaining batter. When each waffle is done, remove using either tongs or a fork.