In a large pot over medium heat, brown the ground beef until fully cooked. Drain excess fat and add the diced onion and minced garlic. Sauté for about 3 minutes until the onion is translucent.

Add the beef broth, diced potatoes, carrots, celery, Worcestershire sauce, mustard, salt, and black pepper to the pot. Bring to a boil, then reduce heat and let simmer for about 15-20 minutes, or until the vegetables are tender.

Stir in the shredded cheddar cheese, milk, and sour cream. Cook for an additional 5 minutes, stirring until the cheese is melted and the soup is heated through.

Serve hot, garnished with chopped green onions if desired.