In a large pot or Dutch oven, melt butter over medium heat. Add carrots, celery and onion; cook until soft.
Stir in the flour; cook 1 minute. Slowly pour in the broth, stirring constantly. Bring to a boil, and cook for 1-2 minutes while stirring frequently.
Add remaining ingredients and bring back to a boil. Reduce heat to simmer and cook uncovered for 15-20 minutes, stirring occasionally.