Add egg, bacon drippings. Slowly ad buttermilk until the mixture is soupy (sort of like cake batter, maybe a little thinner.)
Grease iron skillet with bacon drippings, enough to give it a nice even coat. Put the greased iron skillet in the oven until it is really hot - a few minutes, before pouring in the batter. Bake at 400 for 30-40 minutes.
I suppose you could make this in another oven safe dish, but I'm not sure how long you would cook it.