Preheat oven to 425 degrees F. Place an oven-proof 10-inch cast iron skillet in the oven.

In a large bowl, combine cornmeal, flour, sugar, baking powder and salt.

In a large glass measuring cup or another bowl, whisk together buttermilk, egg and 3 tablespoons butter. Pour mixture over dry ingredients and stir using a rubber spatula just until moist.

Remove skillet from the oven and add remaining 3 tablespoons until heated through, about 1-2 minutes.

Working carefully, immediately scoop the batter into the hot skillet. Place into oven and bake for 25-30 minutes, or until a tester inserted in the center comes out clean. Let cool 5 minutes.

Serve warm.