Cut up one large bunch of celery; boil about 5 minutes; leave crisp. Drain well and put in greased casserole. Cut up and drain 1 can water chestnuts. Add to celery. Put in small pan 1 tablespoon butter; add 1/2 cup slivered almonds and 1 diced medium onion. Brown slightly. Add to celery and water chestnuts. Stir in 1 can cream of chicken soup, undiluted. Bake 1/2 hour. Serves 6.