Wash mushrooms; slice half of them and set aside. Chop remaining mushrooms and saute them in 1 tb margarine in a large pot. Add all the vegetables (except the sliced mushrooms) and cook 6-7 minutes, stirring often. Stir in all other ingredients except the mushrooms, the remaining margarine, and the sherry. Simmer, covered, for 1 hour. Puree soup in the blender or food proscessor fitted with steel blade. Saute the sliced mushrooms in the remaining 1 tb of margarine. Return pureed soup to pot; and sauteed mushrooms and sherry. Reheat over moderate heat, stirring. Food Exchanges per serving: 2 VEGETABLES EXCHANGES + -20ºC AT EXCHANGE CHO: 12g; PRO: 5g; FAT: 5g; CAL: 108; Low-sodium diets: Omit salt. Substitute unsalted beef broth and unsalted margarine.