Step 1

In a large mixing bowl, whisk together the flour, sugar, cornstarch, salt, baking soda, and baking powder. Add the buttermilk, egg, egg whites, and vanilla and stir with a rubber spatula until barely combined. Pour in the melted butter and stir until just combined.

Step 2

Cover the batter and let rest for 15 to 30 minutes.

Step 3

Preheat oven to 250°F. Heat the waffle iron to medium, following the manufacturer's directions.

Step 4

For 8-inch square waffles, ladle about 1/3 cup to 1/2 cup batter into each cavity. Be careful not to overfill or you’ll end up with cakey waffles. Close lid of the waffle maker and cook until deeply golden brown on both sides, about 6 minutes or as long as manufacturer specifies.

Step 5

For 7-inch Belgian waffles, scoop 1/2 to 3/4 cup batter into each cavity, close the iron and flip. Cook until the waffles are deeply golden brown and crisp on both sides, about 7 minutes.

Step 6

Place finished waffles on a wire rack set on a rimmed baking sheet in the warm oven until ready to serve.

Step 7

Don’t lift the lid while cooking. If there’s still noticeable steam coming out of the iron, the waffle isn’t done cooking yet.