Heat butter in a medium pot over medium heat. Add the onion and cook until tender, about 3-5 minutes.
Add the heavy cream, cream cheese, and cheddar cheese. Stir frequently until the cheese is melted and everything is well combined, about 2-4 minutes.
Add the can of drained tomatoes and chiles, along with the salt, pepper, and cumin. Stir and cook until everything is warm and well combined, about 1-2 minutes.