In dutch oven or soup pot, bring chicken broth to a boil. Add broccoli, celery and carrots; boil for 2-3 minutes. Drain pot, carefully reserving liquid, and set vegetables aside. In same pot, sauté onion in butter until tender. Stir in flour to form a smooth paste. Gradually add the reserved broth and milk, stirring constantly. Bring to a boil and stir for 1 minute. Add vegetables and remaining ingredients. Reduce heat, cover and simmer for 30-40 minutes, or until vegetables are tender. Serves 6-8.