In 4-quart microwavable casserole dish, combine celery, onion, potato, carrot, and margarine. Cook, covered, on high power 6 minutes, stirring after 3 minutes. Stir in fresh tomatoes, canned tomatoes with liquid, and bay leaf. Continue cooking, covered, 20 minutes or until potato is fork tender, stirring once or twice. Discard bay leaf. In blender or food processor, puree one third of the mixture at a time. Return puree to casserole; add chicken broth, milk, basil, Sweet’N Low, and pepper. Cook on high power 6 to 7 minutes or until well blended. If a thinner consistency is desired, add additional milk or chicken broth. Adjust seasonings, if desired. Serve hot or cold.