Combine potatoes, onion, celery, 1 teaspoon salt and boiling water in covered kettle. Simmer until tender. Meantime, melt margarine. Stir in flour, then add salt. Add next 4 ingredients while stirring. Cook until thickened, then add cheese and stir until melted. Stir into potato mixture, then add parsley and tomatoes. Heat and serve. (Shrimp, if added, could make this a party soup!)