Preheat oven to 450°F. Generously butter a 9- by 9-inch baking pan.
Whisk together flour, cornmeal mix, sugar, and salt in a bowl. Whisk together buttermilk, eggs, melted butter, and 1 cup Cheddar in a second bowl. Add wet ingredients to dry ingredients and stir to combine. Transfer to prepared baking pan. Sprinkle with remaining ½ cup Cheddar. Bake until golden brown, 20 to 25 minutes.
