Heat an 8-inch cast iron skillet in the oven while you preheat the oven to 425°F.
Meanwhile, in a large bowl, whisk together the buttermilk, egg, and oil.
Add the cornmeal mix and sugar; stir just until combined. Do not overmix – the batter will be lumpy, which is fine.
Once the oven comes to temperature, carefully remove the skillet. Place the butter in the skillet; use a knife or brush to spread the butter on the bottom and sides of the pan until it melts.
Pour the batter into the buttered skillet.
Bake for about 25 minutes, or until a toothpick inserted in the center comes out clean.
