Preheat waffle maker on medium-high heat. Preheat oven to 200°F (93°C). Place a wire rack on a baking sheet; set aside.

In a large bowl preferably with a pour spout, whisk the flour, baking powder, baking soda, and salt together. Set aside.

In another large bowl, whisk the egg yolks, melted butter, and sugar together. Whisk in the buttermilk and vanilla until combined. Pour the wet ingredients into the dry ingredients and then whisk gently until combined. Do not over-mix. Some small lumps are OK.

With a handheld or stand mixer fitted with a whisk attachment, whip the egg whites on high speed until fluffy soft peaks form, about 3 minutes. With a spatula, gently fold the egg whites into the batter.

Grease the preheated waffle maker (I use nonstick spray). Pour about 1/3 cup of the batter into each well of the waffle maker (or less if your waffle maker is smaller) and close the lid. Cook the waffles until crisp, about 4–5 minutes. (Follow the cooking instructions for your waffle maker.) Transfer the cooked waffles to the wire rack and keep warm in the preheated oven as you cook the rest. Repeat to cook the remaining batter.

Serve the waffles immediately with butter and maple syrup, or your choice of toppings.