Saute celery and onion in butter in a Dutch oven for 5 minutes or until tender.
Add garlic, and saute an additional minute.
Stir in potatoes, parsley, and broth.
Bring to a boil; cover, reduce heat, and simmer 20 minutes or until the potatoes are tender.
Pour half of celery mixture into container of electric blender; process 45 seconds.
Repeat with remaining celery mixture.
Stir in seasonings.