Brown the beef: In a large pot or Dutch oven over medium-high heat, brown the ground beef with the onion, breaking it up as it cooks, about 6-8 minutes. Drain off the excess grease.
Bloom the spices: Add the garlic, chili powder, cumin, oregano, salt, and pepper directly to the pot. Stir and cook for about 60-90 seconds until fragrant.
Add the rest: Stir in the diced tomatoes, tomato sauce, kidney beans, pinto beans, and beef broth.
Simmer: Bring to a simmer, then reduce the heat to low and cook uncovered for 30-45 minutes, stirring occasionally, until thickened to your liking.
Serve: Ladle into bowls and top with shredded cheddar.
Notes
Bloom the chili powder and cumin in the hot beef fat for about a minute before adding any liquid, it's what gives this chili real depth instead of a flat, dusty taste.