Preheat your waffle iron: If you have a Belgian waffle maker, preheat according to the manufacturer’s instructions.
Mix dry ingredients: In a medium bowl, whisk together flour, baking powder, baking soda, salt, and sugar.
Separate the eggs: Place egg yolks in one bowl and egg whites in another.
Combine wet ingredients: In a large bowl, whisk egg yolks, milk, melted butter, and vanilla until smooth.
Add dry to wet: Gently whisk dry ingredients into the wet ingredients until just combined—don’t overmix. The batter should still have a few lumps.
Whip the egg whites: Using an electric mixer, beat egg whites until stiff peaks form. This step is key for fluffy waffles.
Fold the egg whites into the batter: Use a spatula to gently fold, not stir, the whipped egg whites into the batter to keep the air pockets intact.
Cook the waffles: Pour batter into the preheated Belgian waffle iron, spreading to the edges. Close and cook until golden brown—usually 4–5 minutes.
Serve immediately: Top with powdered sugar, whipped cream, syrup, or whatever your heart desires.