In a large saucepan, saute zucchini and onion in butter for 5-6 minutes or until tender. Stir in broth. Bring to a boil. Reduce heat; cover and simmer for 12-15 minutes. Cool slightly.
Transfer to a food processor; cover and process on low until smooth. Return to the pan. Stir in the cream, salt, basil, pepper and nutmeg. Bring to a boil. Reduce heat; simmer, uncovered, for 1-2 minutes or until heated through. Garnish with sour cream and additional nutmeg if desired. Yield: 6 servings.