Preheat oven to 400°F (200°C). Grease a 9-inch cast iron skillet.
In a medium bowl, combine cornmeal, flour, baking powder, baking soda, sugar and salt. In a separate bowl, mix together egg, buttermilk and melted butter.
Slowly stir wet ingredients into dry ingredients until just combined. Pour batter into prepared skillet.
Bake for 20 minutes or until golden brown. Serve warm.