Place the flour, cornstarch, sugar, baking soda, baking powder, and salt in a large bowl and whisk to combine. Make sure the cornstarch is evenly distributed with no clumps.

In a separate bowl, combine the egg, half-and-half, buttermilk, and vanilla and whisk until smooth. Slowly drizzle in the melted butter while whisking constantly to prevent it from solidifying when it hits the cold dairy.

Pour the wet mixture into the dry ingredients. Stir gently with a rubber spatula just until combined. Do not overmix. It is perfectly fine (and preferred) if small lumps remain in the batter.

Cover the bowl tightly with plastic wrap and place it in the refrigerator overnight.

The next morning, preheat your waffle iron. To achieve a golden-brown crust, lightly brush the waffle iron plates with melted butter or spray with cooking spray before adding the batter.

Scoop approximately 1/2 to 2/3 cup of batter (depending on your iron size) onto the preheated waffle iron plate. Close the iron and cook until the steam stops rising, about 4 to 6 minutes. The waffles should be golden and crispy on the outside but tender on the inside.