Heat a large pot over medium heat and add the ground beef, onion, and garlic. Cook until the beef is browned and the onion softens.
Stir in the tomato sauce, kidney beans, chili powder, cumin, salt, and black pepper. Bring to a simmer and cook uncovered for 20 minutes, stirring now and then, until the chili thickens.
While the chili simmers, preheat the oven to 400°F and grease an 8-inch square baking dish.
In a mixing bowl, combine the cornmeal, flour, baking powder, and sugar. In a separate bowl, whisk together the milk, egg, and vegetable oil.
Pour the wet mixture into the dry ingredients and stir just until combined. Spread the batter evenly in the prepared dish.
Bake the cornbread for 20 minutes until the top is golden and a toothpick inserted in the center comes out clean. Cut into squares and serve warm with the chili.