Preheat oven to 400℉. Grease a 9 inch cast iron skillet or glass dish. Place dish in heated oven while you make the cornbread mix.
In a mixing bowl, combine cornbread mix, buttermilk, and an egg. Whisk until evenly combined. Optional: mix in vegetable oil.
Carefully remove your skillet or dish from the oven. Using a rubber spatula, dump the mixture into the dish, scraping the sides to get it all. Bake for 25 - 30 minutes.