Preheat oven to 375-degrees and grease the cast-iron skillet with butter.
Place the skillet in the oven while preparing the cornbread.
In a large bowl, add the cornmeal, all-purpose flour, baking powder, baking soda, and salt and whisk together.
Next, pour the buttermilk, melted shortening, egg, and sour cream into the bowl and mix well.
Take the skillet out of the oven and pour the mixture in.
Place the skillet back into the oven and bake for 20-25 minutes or until a cake tester comes out clean.