Place the butter in a 10†cast iron skillet and place the skillet in the oven. Turn the oven on to preheat to 400 degrees. In a medium mixing bowl, combine the corn muffin mix, chopped green onions, milk, sour cream, and eggs. Mix until thoroughly combined. When the oven has preheated, carefully remove the hot skillet from the oven and pour the cornbread batter into the center of the pan. Return to the oven and bake for 25-30 minutes.