Melt one stick butter in oblong casserole. Pour almost all melted butter into a bowl leaving casserole well coated. Combine with the butter in the bowl: celery soup, milk, mayon- naise and onion. In buttered casserole, crumble slightly a layer of corn flakes. Add shredded cabbage. Place sliced water chestnuts over cabbage layer. Pour soup mixture over cabbage. Crumble another layer of corn flakes on top. Bake at 350 degrees for 45 minutes. Serves 10 to 12.