Sift together the flour, sugar, baking powder and salt into a mixing bowl.
Beat the egg yolks until pale yellow, then combine with the milk.
Pour the egg and milk mixture into the flour and stir until smooth.
Add the melted butter or bacon fat and blend thoroughly.
Set aside and allow to stand for at least an hour.
Beat the egg whites until stiff and fold into the batter.
Fill a hot lightly oiled waffle iron two-thirds full with the batter and cook until steam stops escaping from the sides.