Preheat oven. Preheat the oven to 375℉.
Cook beef and onion. In a large skillet or Dutch oven, cook the ground beef over medium-heat, breaking it into smaller pieces as you cook, for 5-7 minutes until browned. Add onion and cook another 5 minutes until the onion becomes softened and looks translucent. Add minced garlic and cook for an additional minute. Drain excess grease.
Add seasonings. Add chili powder, salt, cumin, oregano, brown sugar, and pepper and stir into the meat mixture to season.
Add beans, broth, and chilies. Stir in chili beans, tomato sauce, diced tomatoes, chicken broth, green chilies, and corn. Simmer for 10-15 minutes while you prepare the cornbread.
Make cornbread. In a medium-sized bowl, mix the cornbread mixes, milk, and eggs until fully incorporated.
Cover chili with cornbread. Pour the chili into a 9x13 baking pan and use a spatula to spread the chili in an even layer. Pour enough cornbread mix on the chili to cover it and spread evenly over the chili. (I only use about ¾ of the cornbread mixture).
Bake. Place in the oven and bake for 30 minutes or until golden brown on top.
Cool. Let it rest for 10 minutes after removing from the oven, and then serve immediately with optional toppings.