In Dutch oven, saute onion, garlic, and thyme until onion is softened. Add beef, potatoes, carrot, and celery until beef is brown. Add tomato paste, mustard, and worcestershire sauce for 2 minutes, until thickened. Stir broth, pepper, and salt and bring to boil. Cover and simmer until potatoes are tender. Stir in peas, until warm.