Step 1: In a large mixing bowl, whisk together the flour, sugar, baking powder, baking soda, and salt. Make sure all dry ingredients are well combined.
Step 2: In a separate medium bowl, whisk together the buttermilk, melted butter, and vanilla extract. Add the egg yolks to this mixture and whisk until smooth.
Step 3: In a clean, dry bowl, beat the egg whites with an electric mixer until stiff peaks form.
Step 4: Pour the wet ingredients into the dry ingredients. Mix gently with a spoon or spatula until just combined. Do not overmix; a few lumps are fine.
Step 5: Gently fold the beaten egg whites into the waffle batter using a rubber spatula. Be careful not to deflate the whites, as they contribute significantly to the waffle's fluffiness.
Step 6: Preheat your waffle iron according to the manufacturer's instructions. Lightly grease it with cooking spray or a brush of melted butter if needed.
Step 7: Pour about 1/2 to 3/4 cup of batter (depending on your waffle iron size) onto the hot iron. Close the lid and cook for 3-5 minutes, or until the waffle is golden brown and crispy.
Step 8: Carefully remove the cooked waffle and serve immediately with your favorite toppings. Repeat with the remaining batter. Keep finished waffles warm in a 200°F (95°C) oven on a wire rack.