In a large saucepan bring beef broth and the 2 1/2 cups water to boiling. Stir in barley, onion, garlic, dried basil (if using), Worcestershire sauce, and pepper. Cover and simmer 5 minutes. Stir in mushrooms and carrot. Simmer, covered, about 5 minutes more or until barley is tender.
Meanwhile, in a small bowl combine cornstarch and the 2 tablespoons water; stir into saucepan. Cook and stir until slightly thickened and bubbly. Cook and stir 2 minutes more. Stir in fresh basil, if using. Sprinkle with parsley. Makes 4 servings.