Preheat your Belgian waffle maker according to manufacturer instructions.
In a large bowl, whisk together flour, sugar, baking powder, and salt.
In another bowl, beat egg yolks and gradually add milk, melted butter, and vanilla extract, whisking until combined.
Pour the wet ingredients into the dry ingredients and mix until just combined. Do not overmix; some lumps are okay.
In a separate clean bowl, beat egg whites until stiff peaks form.
Gently fold the beaten egg whites into the batter until just incorporated.
Pour the batter onto the preheated waffle maker and cook according to manufacturer instructions until golden brown and crispy.
Serve warm with your favorite toppings such as maple syrup, fresh fruit, whipped cream, or chocolate sauce.