Preheat your Belgian waffle maker according to manufacturer's instructions.
In a large bowl, whisk together flour, sugar, baking powder, and salt.
In a separate bowl, beat egg whites until stiff peaks form. Set aside.
In another bowl, whisk together egg yolks, milk, melted butter, and vanilla until well combined.
Pour the wet ingredients into the dry ingredients and stir until just combined (batter will be slightly lumpy).
Gently fold in the beaten egg whites until incorporated.
Pour batter onto the preheated waffle iron and cook according to manufacturer's directions until golden and crispy, about 4-5 minutes per waffle.
Serve immediately with butter, maple syrup, fresh berries, or whipped cream.