Preheat a Belgian waffle maker. Grease only if recommended by machine manufacturer. Combine the egg yolks, milk, flour, baking powder, salt, and oil in a large mixing bowl. Beat on low speed with a mixer until mixed. Increase mixer speed to medium and beat until smooth and no clumps of flour remain. By hand, gently fold in the beaten egg whites. Using a half-cup measure, pour the batter onto the waffle maker grids. Close the top and cook until steam no longer escapes, about 3-5 minutes. Repeat with remaining batter. Serve hot with your favorite toppings. Variations: Pecan or Macadamia Nut Waffles: Sprinkle 1 Tbsp. finely chopped pecans or macadamia nuts over preheated waffle grids. Pour 1/2 cup batter over nuts and close waffle maker. Bake as directed. Blueberry Waffles: Fold 2 c. fresh blueberries into batter. Pour 3/4 cup batter over grids. Bake as directed. Chocolate Chip Waffles: Fold 1 cup chocolate chips into batter. Bake as directed.