Preheat the oven to 450 degrees. Put the drippings in a 9-inch cast iron skillet. Place the skillet in the oven and let the drippings heat while you prepare the batter. In a big bowl, mix the cornmeal, salt, and baking soda. Add the egg and buttermilk, and stir until just blended. The drippings should be good and hot, but not smoking, by now. Carefully remove the skillet from the oven and swirl gently to coat it with drippings. Pour the rest of the drippings into the batter. It should crackle and pop. Mix quickly and lightly, just to blend, then pour the batter into the skillet and put it back in the oven. Bake 20 to 25 minutes, until the bread is set in the middle, the edges are browned, and the top crust is golden. Serve hot, cut into wedges and lifted straight out of the skillet. If you prefer, turn the skillet upside down and let the cornbread slip out on a big plate. If your cast-iron is seasoned well, it will do so easily.