Roast the chiles under the broiler until blackened on both sides, about 10-12 minutes, turning once. Once blackened, place the chiles in a paper sack or plastic food-storage bag, close it tight and let the chiles steam for 20 minutes. After the chiles have steamed, remove from the bag and rub off the skin. Remove the stems and seeds from the chiles and chop. You should have about 1 cup.
Preheat oven to 450° F. While the oven is heating, put the bacon grease or oil into a 10-inch cast-iron skillet and place in the oven while the oven preheats.
Meanwhile, mix together the cornmeal, flour, baking powder, baking soda, and salt. Whisk together the eggs and buttermilk and pour into the dry ingredients. Stir until well combined.
Take the cast iron skillet out of then oven, and pour the hot oil into the batter and stir until well combined. Add the Hatch green chiles to the batter and gently stir until evenly distributed.
Pour the batter back into the hot skillet and bake for 18-20 minutes or until the top is lightly browned and an inserted knifes comes out clean. Serve warm.
Notes
If you don't have access to fresh green chiles for roasting, or have roasted ones already, use 1 cup of chopped green chiles. You may also substitute a 4-ounce can chopped green chiles with its juices.