Step 1

Place butter in a 13- x 9–inch glass or ceramic baking dish. Place dish in oven; preheat oven to 375°F (leave dish in oven as it heats).

Step 2

Combine blueberries, 1/2 cup sugar, cornstarch, and lemon juice in a large bowl, tossing well to coat.

Step 3

Whisk together flour, cornmeal, baking powder, salt, baking soda, and 3/4 cup plus 2 tablespoons sugar in a medium bowl. Add buttermilk and vanilla to flour mixture; stir until well combined.

Step 4

Carefully remove baking dish from oven. Arrange blueberry mixture over butter; pour batter over blueberries. Sprinkle remaining 2 tablespoons sugar evenly over batter. Bake at 375°F until filling is bubbly and topping is browned, 40 to 45 minutes.