In a large pot, heat olive oil over medium heat. Add the ground beef, onion, and garlic. Cook until the beef is browned and the onions are translucent, about 5-7 minutes. Drain excess fat if necessary.

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 simmer for 15-20 minutes, or until the vegetables are tender.

In a small bowl, whisk together the milk and flour until smooth. Slowly add this mixture to the soup, stirring constantly. Cook for an additional 5 minutes until the soup thickens slightly.

Remove the pot from heat and stir in the shredded cheddar cheese until melted and well combined.

Serve hot, garnished with fresh parsley.