Saute mushrooms and onions in butter in non-stick skillet until tender. Place chicken breasts on top of mushroom mixture, cover and cook over medium heat 7 minutes or until chicken is cooked and juices run clear. Slice chicken diagonally and place on serving platter; keep warm. Add cream, mustard, and seasonings to pan drippings. Reduce liquid until thickened. Add grapes; heat thoroughly. Pour over chicken. garnish with grape cluster and marjoram. Recipe By : Bon Appetit