Preheat the oven to 400 degrees. Prepare a 9 or 10" cast iron skillet with the butter/shortening by rubbing a thin layer all over the inside of the pan. Place the pan into the oven on a center rack while the oven preheats. Once oven is preheated, allow pan to stay in the oven another 5 minutes.
In a large bowl, mix together the corn meal mix, whole milk, large egg, vegetable oil and salt and pepper. Mix very well removing all lumps. Use a whisk if lumps are a problem
Once the oven has come to temp, allow the skillet to remain in the oven for a few more minutes. Gather together the following items at the stove: Cornbread batter, good hot pad/oven mitt, rubber spatula.
As quickly as possible, open the oven, pull the rack that the pan is sitting on out where you can easily pour the batter into the pan without getting burned (use your oven mitt). Use the rubber spatula to quickly scrape all of the cornbread batter into the skillet. You should hear some sizzling (that is good because that is a crusty bottom on your cornbread developing!).
Using your oven mitt, push the rack and skillet back into the oven and shut the oven door and don't dare open it again for at least 15 minutes. The cornbread is done when it has risen and is golden across the surface. You will probably notice some C shaped cracks near the edges of the cornbread and that is fine.
When done, remove from the oven and serve right away. Hot butter is the best garnish! :)