Prepare the filling: In a large skillet over medium heat, brown the ground beef with the chopped onion, stirring until crumbly and fully cooked. Drain excess fat if needed.
Season and simmer: Stir in the tomato soup, green pepper, chili powder (if using), black pepper, kidney beans, corn, and 1 teaspoon of salt. Mix well and let the mixture simmer gently for about 15 minutes.
Assemble the casserole: Spoon the meat mixture into a greased 2-quart casserole dish, spreading it evenly.
Make the cornbread topping: In a bowl, combine the cornmeal, flour, baking soda, and remaining 1 teaspoon of salt. Add the beaten egg, buttermilk, and bacon drippings. Stir just until combined.
Top and bake: Spoon the cornbread batter evenly over the meat mixture.
Bake: Bake at 350°F for 30–40 minutes, or until the cornbread topping is set and lightly golden.
Rest and serve: Let the casserole rest for 5–10 minutes before serving.