In a large pot or Dutch oven, cook the ground beef and chopped onion over medium-high heat until the beef is browned and the onion is softened. Drain off any excess grease.
Add the minced garlic and cook for 1 minute more until fragrant.
Stir in the diced tomatoes, black beans, kidney beans, corn, Rotel, taco seasoning, chili powder, cumin, and beef broth.
Bring the soup to a boil, then reduce heat and simmer for at least 20 minutes, or up to 1 hour, stirring occasionally.
Stir in the heavy cream and shredded cheddar cheese. Heat through until the cheese is melted and the soup is creamy. Do not boil after adding cream.
Serve hot, garnished with your favorite toppings.
Notes
For a spicier soup, use a hotter variety of Rotel or add a pinch of cayenne pepper.
If you prefer a thicker soup, you can mash some of the beans against the side of the pot before adding the cream.
This soup freezes well. Let it cool completely before transferring to freezer-safe containers.