In a large saucepan, saute the onion, carrots, and celery in butter until
tender. Stir in potato soup and clams, undrained. Combine cornstarch and a small amount of cream until smooth. Stir in soup. Add remaining cream. (I use 1 pint of half and half and 1 pt. milk.) Bring to a boil. Cook about 2 minutes or until thickened.