1. Heat the oil in a large saucepan over medium heat. Add the onions and cook for 5 minutes, or until softened. Add the garlic and cook 1 minute. Stir in the chile powder and cumin, then the beef. Cook, breaking up the beef with a spoon, until it browns all over, about 5 minutes.

2. Stir in the beans, tomatoes, and tomato paste and bring to a boil. Reduce the heat, cover, and simmer for 40 minutes, stirring occasionally, until thickened. Season with salt and pepper. Serve hot, sprinkled with cilantro and topped with sour cream.