Preheat the oven to 400ºF.
For the cornbread layer, in a medium bowl, combine the Jiffy cornmeal muffin mix, egg, sour cream, canned cream corn, and chopped jalapeños (if using). Mix until just combined.
Butter a 12-inch cast-iron skillet or 13"x9" baking dish with ½ tablespoon of the butter. Pour the mixture into the prepared dish. Bake 20 minutes or until golden brown.
For the beef mixture, in a large skillet, heat the remaining butter over medium-high heat. Add the chopped onion and cook until softened, about 5 minutes.
Add the ground beef to the skillet. Crumble and cook until no longer pink. Drain any excess fat. Season with fresh garlic, cumin, chili powder and seasoning salt or salt, black pepper. Cook for another minute.
Carefully remove the cornbread base from the oven. Poke holes all over the surface.
Pour half of the can of enchilada sauce over the cornbread. Top with the beef mixture, spreading out evenly. Pour remaining enchilada sauce over the beef mixture and top with shredded cheese.
Cover with aluminum foil and bake for 20 minutes. Uncover and broil on high an additional 3-5 minutes. Remove from the oven and allow to cool for 10 minutes (otherwise it will fall apart when serving).
Garnish with olives, guacamole, pico de Gallo, sour cream, and/or salsa.