Grease and preheat your waffle iron according to the manufacturer's instructions., In a large bowl, beat together the egg yolks, buttermilk, butter and oil until well combined., In a separate bowl, sift or whisk together the dry ingredients., Gently stir the dry ingredients into the wet ingredients. Don't beat the batter; it's unnecessary, and will make for tougher waffles., Beat the egg whites until stiff. Gently fold them into the batter., Bake the waffles according to your waffle iron's instructions. To keep finished waffles crisp as you continue baking, place them in a preheated 200°F oven, directly on the rack.