Preheat the oven to 425 degrees.
As the oven is preheating, prepare the pan. Put 3 tablespoons of cooking oil into a 9 or 10 inches cast iron skillet.
Place the pan into the oven to heat.
You want the pan and the oil to be sizzling hot when you put the cornmeal batter into the pan. This will create an amazing crust for the cornbread. If you don’t have a cast-iron pan, a heavy cake pan or cooking pan will do.
As the oven is heating, stir together the cornmeal, flour, baking powder, baking soda, salt, and sugar in a medium-sized bowl.
In a separate small bowl, beat the egg lightly with a fork.
Stir in the buttermilk and the cooking oil.
Next, add the bowl of wet ingredients to the bowl of dry ingredients.
Using a fork, stir these things together, just until they are incorporated.
You do not want to overmix this batter, because that will lead to a tougher cornbread. You just want the dry ingredients moistened, and it is okay if there are a few lumps in the batter.
Using an oven mitt, carefully remove the hot pan with the layer of hot oil from the oven.
Set it on a heatproof surface and slowly pour the batter into the pan. It should sizzle as you put the batter into the oil. That’s okay! It’s just the batter starting to cook into a nice, crisp, golden-brown crust on the surface of the cornbread.
Return the pan to the oven and bake it for 15 to 20 minutes, or until the surface of the cornmeal is lightly browned.
Remove the pan from the oven.
Let the cornbread cool for about 5 minutes, and run a knife around the outer edge of the pan to loosen the cornbread cake.
Then, quickly, using a snap of the wrist, turn the pan over onto a plate to remove it from the pan.
Slice the cornbread into six or eight wedges and serve.