In a large saucepan saute garlic and onion in butter until translucent. Add broth, potatoes, carrots, celery (without tops) and zucchini. Bring soup to a boil and simmer for 15-20 minutes or until potatoes are just tender.
Add dill, parsley, pepper (salt), celery tops and the thickener, if desired. Simmer until slightly thickened. Serve immediately with croutons if you like. Makes 6 servings.
This is a light, yet hearty soup and goes well with salmon or tuna sandwiches for a quick, easy meal.