Place chipotle chile in a small pot and add 1/2 cup of water. Bring to a boil, cover and remove from heat until cool. When cool, remove stem and seeds from chipotle and chop finely.
In a large bowl, combine the cornmeal, flour, baking powder, sugar, salt and baking soda. Melt the butter in a medium skillet over medium heat. Cook the onions until soft, about 5 minutes. Add chopped chipotle and set aside.
Grease a cast iron skillet (6 inches in diameter and at least 1inch deep), with 1 teaspoon of the shortening and heat skillet in a 450 degree oven for 10 minutes. Add the remaining shortening to the cornmeal mixture and blend until it resembles coarse crumbs. Add the onion mixture and gradually stir in the buttermilk so that batter that barely holds its shape. Stir until just mixed.
Pour batter into the hot skillet and bake it in the middle of a 450 degrees oven for 10 to 12 minutes. Cool for 5 minutes in the pan. Place a rack over the skillet, turn skillet over and invert bread onto rack.
c.1996, M.S. Milliken & S. Feniger, all rights reserved