In a large bowl, combine flour, granulated sugar, brown sugar, baking powder, and salt.
Separate egg yolks from egg whites. In a separate bowl, lightly beat egg yolks. When melted butter has cooled enough to touch but is still melted, combine with room temperature milk and vanilla. Mix well, then combine with beaten egg yolks.
Using a stand mixer with the whisk attachment, beat egg whites until soft peaks form and can just barely hold their shape. Take care not to over or under mix them.
Transfer wet ingredients (milk, butter, egg yolk, vanilla mixture) to the dry ingredients and stir by hand to combine. Add beaten egg whites and fold them into the mixture. Take care to gently mix in order to fully incorporate but also keep as much air in the mixture as possible.
Bake in a preheated waffle iron according to manufacturer's directions until golden brown.