Preheat oven to 200 degrees F. Heat waffle maker to highest setting.
Mix the flour, cornstarch, baking powder, salt and sugar using a whisk to combine well.
Beat the egg yolk with a whisk until smooth. Stir in the milk, vanilla, and butter.
Combine the milk mixture with the dry ingredients. Stir until mostly smooth.
Beat the egg whites until stiff peaks form using an electric mixer or blender.
Carefully but thoroughly fold the egg whites into the batter. Cook waffles according to waffle maker instructions.
Place waffles directly on the oven racks until ready to serve. (And don't stack them!)
