Basic Belgian Waffles

4 eggs, separated, at room temperature
1 tablespoon sugar
1/4 cup butter or margarine, melted and cooled
1 cup milk
1 teaspoon vanilla (optional)
2 cups flour
2 teaspoons baking powder
1/2 teaspoon salt (optional)

Beat egg yolks and sugar in a bowl until light. Add cooled, melted butter or margarine, milk, and vanilla extract. Add flour, baking powder, and salt. Beat well. Beat egg whites until stiff and gently fold into batter.