Heat margarine in skillet, over medium heat. Saute onion until tender. Stir in whipping cream, heat to boiling. Stir in remaining ingredients. Reduce heat to low. Cover and simmer for 30 minutes, Stirring often. Makes about 3 1/2 cups. Serve with up to 6 servings of hot fettucini. (6 servings = 12 oz dry pasta or 2 oz. Per serving).