Prepare the oven: Preheat oven to 375°F (190°C). Lightly grease a 9×13-inch baking dish.
Brown the beef: Heat a large skillet over medium-high heat. Add ground beef and onion. Cook for 6–8 minutes, breaking up the beef, until browned and the onion is softened. Drain excess grease if needed.
Add flavor: Stir in garlic and cook for 30 seconds. Add kidney beans, corn, diced tomatoes with green chiles, tomato paste, chili powder, cumin, smoked paprika, salt, and black pepper. Cook for 3–4 minutes.
Add cheese: Remove from heat and stir in 1 cup Cheddar cheese until incorporated.
Make the topping: In a bowl, combine Jiffy corn muffin mix, egg, milk, sour cream, and corn. Stir just until combined; do not overmix.
Assemble: Spread the beef mixture evenly in the prepared baking dish. Spoon the cornbread mixture over the top and spread evenly.
Top with cheese: Sprinkle the remaining ½ cup Cheddar cheese over the cornbread layer.
Bake: Bake uncovered for 30–35 minutes, or until the cornbread is golden and cooked through. A toothpick inserted into the center should come out mostly clean.
Rest: Let the casserole rest for 5–10 minutes before serving.