Whisk together flour, cornstarch, salt, baking powder, and baking soda in a bowl.

Whisk together egg, sugar, butter, and vanilla in a separate large bowl until mixture is smooth. Whisk in half-and-half and buttermilk. Add flour mixture; stir until just combined and a few lumps remain. (Do not overmix.) Chill, covered, at least 1 hour or up to overnight.

Preheat waffle iron to medium-high; lightly coat with cooking spray. Pour about 2/3 cup batter onto waffle iron. Cook until golden and crisp on edges, 4 to 6 minutes. Transfer to a plate; keep warm. Repeat with remaining batter.

Serve waffles with maple syrup, chocolate chips, and/or additional butter.