Yeast Raised Christmas Waffles

In a small bowl, dissolve yeast in warm milk. Let stand until creamy, about 10 minutes. In a large bowl, mix the flour, salt, and sugar. Beat the egg yolks into the yeast mixture, and mix into the dry ingredients. Stir in the vanilla extract and melted butter. In a large glass or metal bowl, whip egg whites until stiff peaks form. Carefully fold into the waffle batter. Let stand in a warm place about 45 minutes, or until doubled in size. Preheat a Belgian-style waffle iron, and coat with cooking spray. Place 3/4 to 1 cup of batter onto the hot iron; close the lid. Cook until the steaming subsides and the waffle is golden brown.