Brown the ground beef in a skillet over medium heat with the diced onion and minced garlic until the beef is no longer pink. Drain any excess fat.
Transfer the beef mixture to the slow cooker. Add the kidney beans, black beans, diced tomatoes, beef broth, smoked paprika, chili powder, cumin, salt, and black pepper. Stir to combine.
Cover and cook on low for 6 to 7 hours or on high for 3 to 4 hours until the flavors have melded.
About 30 minutes before the chili is done, preheat the oven to 400°F. In a mixing bowl, whisk together the cornmeal, flour, baking powder, milk, egg, and melted butter until just combined.
Pour the cornbread batter into a greased 8-inch baking dish and bake for 18 to 20 minutes until the top is golden and a toothpick comes out clean.
Serve the chili hot with squares of warm cornbread on the side.