Preheat your oven to 425 °F.
Placea10-inch ovenproofcast-iron skillet in the oven while preheating.
In a large bowl, add the cornmeal, flour, sugar, baking powder and salt and with awire whisk, mix well.
In another large bowl, add buttermilk, 3 tablespoons of butter and egg andwhiskuntil well blended.
Add the buttermilk mixture into the bowl of flour mixture until just blended.
Carefully remove the hot skillet from oven.
Immediately place the remaining butter in the hot skillet, place and spared evenly.
Place the mixture into the hot skillet evenly.
Bake for about 25-30 minutes.
Remove the skillet of cornbread from oven and place onto a wire rack to coolfor about 5 minutes.
Now, invert the bread onto the wire rack.
Cut the bread into desired-sized pieces and serve warm.