Pre heat your oven to 450 degrees. Once oven comes to temp, spray cast iron skillet with the non stick spray and put in the oven while preparing the cornbread.
Put your buttermilk into a bowl, beat egg and encorporate this with the milk. Add your oil and your cornmeal mix and sugar and mix until smooth. If your batter is too thick add about a couple tablespoons more buttermilk until it looks creamy and pourable.
Pour your mix right into the cast iron pan. I don't take mine out of the oven, I just pull the rack out and pour it right in.
Bake this for about 20 to 25 minutes. When its done, I let it sit for a couple minutes and take a dinner plate and set it ontop of the skillet and flip it out onto the plate. I love this served warm.