Preheat your waffle iron to its medium-high setting. If your iron doesn't have a non-stick coating, lightly brush or spray it with oil or melted butter.

In a large mixing bowl, whisk together the all-purpose flour, cornstarch, granulated sugar, baking powder, baking soda, and salt until well combined and lump-free.

In a separate medium mixing bowl, whisk the eggs until lightly beaten. Add the whole milk, cooled melted butter, and vanilla extract, whisking until fully incorporated.

Pour the wet ingredients into the dry ingredients. Stir with a whisk or spatula until just combined. A few lumps are okay; do not overmix, as this can lead to tough waffles. Let the batter rest for 5-10 minutes while the waffle iron finishes preheating.

Once the waffle iron is hot, pour about 1/2 to 3/4 cup of batter onto the center of the iron, depending on its size. Close the lid and cook according to your waffle iron's instructions, typically for 3-5 minutes, or until the waffle is golden brown and steam is no longer actively escaping. For extra crispy edges, you might cook for an additional 30 seconds to 1 minute, watching carefully.

Carefully remove the waffle from the iron and serve immediately. For best crispiness, place cooked waffles on a wire rack while you cook the remaining batter, rather than stacking them (which can make them soggy).