Step 1: In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, cornstarch, baking powder, baking soda, and salt until well combined.
Step 2: In a separate medium bowl, beat the eggs and then stir in the buttermilk, melted butter, and vanilla extract until smooth.
Step 3: Pour the wet ingredients into the dry ingredients and gently fold with a spatula until just combined; do not overmix the batter.
Step 4: Let the batter rest for 10 minutes while you preheat your waffle iron to its medium-high setting.
Step 5: Lightly grease the waffle iron and pour about 1/2 to 2/3 cup of batter (depending on your iron size) onto the center. Close and cook until golden brown and the steam has mostly stopped.
Step 6: Remove carefully and serve immediately, or keep warm in a 200°F oven on a wire rack to maintain crispness.