Stir whole-wheat flour, all-purpose flour, baking powder, salt and baking soda in a large bowl. Whisk buttermilk, the egg yolk, oil and vanilla (if using) in a separate bowl. Add the wet ingredients to the dry ingredients and stir with a wooden spoon just until moistened.Advertisement
Beat the 3 egg whites in a grease-free mixing bowl with an electric mixer until soft peaks form. Add sugar and continue beating until stiff and glossy. Whisk one-quarter of the beaten egg whites into the batter. Fold in the remaining beaten egg whites with a rubber spatula.
Preheat a waffle iron. Brush the surface lightly with oil. Fill the waffle iron two-thirds full of batter. Cook until the waffles are crisp and golden, 5 to 6 minutes. Repeat with the remaining batter, brushing the surface with oil before cooking each batch.
No buttermilk? You can use buttermilk powder prepared according to package directions. Or make “sour milk”: the ratio is 1 tablespoon lemon juice or vinegar to 1 cup milk.
2 1/2 other carbohydrate, 1/2 fat