Preheat Waffle Iron: Preheat your Belgian waffle iron according to manufacturer instructions.
Mix Dry Ingredients: In a large bowl, whisk together flour, sugar, baking powder, and salt.
Combine Wet Ingredients: In a medium bowl, whisk together egg yolks, milk, melted butter, and vanilla extract.
Beat Egg Whites: In a separate bowl, beat egg whites until stiff peaks form.
Combine Batter: Pour wet ingredients into the dry ingredients and mix until just combined. Gently fold in the beaten egg whites, being careful not to deflate them.
Cook Waffles: Grease waffle iron lightly with butter or cooking spray. Pour batter onto the center of the waffle iron (amount depends on your waffle iron size) and cook until golden brown and crisp, about 4–6 minutes.
Serve: Serve immediately with syrup, fresh fruit, whipped cream, or your favorite toppings.