In a Dutch oven over medium heat, cook and stir the beef, mushrooms, celery and onion until meat is no longer pink; drain. Stir in flour until blended; gradually add broth. Stir in the carrots, potato, pepper and salt. Bring to a boil. Stir in barley.
Reduce heat; cover and simmer for 45-50 minutes or until barley is tender. Whisk in milk and tomato paste; heat through. Yield: 4 servings.