Step 1

Mix the dry ingredients: In a large mixing bowl, sift together the flour, sugar, baking powder, and salt.

Step 2

Prepare the batter: In a medium-sized mixing bowl, whisk the egg yolks, milk, vinegar, melted butter, and vanilla until well-combined. Add the egg yolk mixture to the flour mixture and stir to just combine, being careful not to overmix; there should be a few small lumps of flour in the batter.

Step 3

Prepare the waffle iron: Preheat a waffle iron according to the manufacturer's instructions.

Step 4

Whip the egg whites: In a perfectly clean stainless steel mixing bowl, beat the egg whites until foamy. Add the cream of tartar, then continue to beat until soft peaks form.

Step 5

Fold the whipped whites into the batter: With a silicone spatula, gently scoop the whipped whipped egg whites into the batter. Then scoop them from underneath, along with some of the batter, very gently turning the whole thing over. Repeat until just incorporated.

Step 6

Cook the waffles: Spoon or pour the batter into the waffle iron and cook according to the manufacturer's instructions, usually for 2 to 3 minutes. (You will need 1/2 to 2/3 cup of batter per waffle for a Belgian or big waffle maker, but the size can vary quite a bit. Consult the manufacturer's instructions for each model for specific guidelines.)

Step 7

Keep the waffles warm: To keep the waffles warm when making a big batch, place a baking rack on a baking sheet and arrange the cooked waffles in a single layer on it. Place in a 200°F oven to keep warm.