Put the bacon drippings in a 9" to 10" cast iron skillet and place in the oven as it preheats to 450°F., Whisk together the cornmeal, flour, baking powder, baking soda, and salt in a medium bowl., In a small bowl, whisk together the egg and buttermilk. Make a well in the center of the cornmeal mixture and pour in the egg mixture. Stir only until blended., Remove the skillet from the oven and pour in the batter. It will sizzle and pop, so be careful., Bake until the cornbread is firm in the middle and golden brown on top, about 25 minutes. Turn out onto a cutting board or cooling rack and serve piping hot.