Preheat oven to 425 degrees with a 10 inch cast iron skillet in it.

Whisk together cornmeal, flour, sugar, baking powder, baking soda, and salt in a large bowl.

In a measuring cup, whisk egg, milk and buttermilk.

Stir the wet into the dry ingredients.

Carefully remove the HOT skillet and add the butter, letting it melt. (will sizzle and brown)

Pour in the batter and bake 23-27 minutes until a toothpick comes out clean and it is golden.