Preheat the oven to 400 degrees F. Heat a 10-inch cast iron skillet in the oven.
Combine all of the ingredients in a bowl, except for the butter, and mix together well with a spatula.
Melt the butter in the hot skillet, then pour off the excess into the batter and mix in well.
Turn the oven down to 375 degrees F (175 degrees C).
Pour the cornbread mixture into the skillet, place in the oven and bake for 30 to 40 minutes, or until a toothpick inserted in the center comes out clean. Let cool slightly, carefully remove from the skillet and place on a wire rack to cool until ready to eat.