Brown the ground beef in a large pot over medium heat. Add the diced onion and minced garlic, then cook until the onion softens.
Stir in the chili powder and cumin. Cook for one minute to toast the spices.
Add the diced tomatoes and kidney beans. Season with salt and pepper. Simmer uncovered for 20 minutes, stirring occasionally.
While the chili simmers, heat the oven to 400°F. In a mixing bowl, combine the cornmeal, flour, and baking powder. In a separate bowl, whisk the egg, milk, and melted butter. Pour the wet mixture into the dry ingredients and stir until just combined.
Spread the batter into a greased 8-inch square pan. Bake for 15 to 18 minutes until the top is lightly golden. Cool slightly, then cut into strips for dipping.
Ladle the chili into bowls and top each serving with shredded cheddar cheese. Serve the cornbread strips on the side.