Slice cabbage coursely in pan. Add salt and barely enough water to cover. Boil uncovered until just barely tender, about 7 minutes. Drain, saving 3/4 cup water for later use. Melt 2 tablespoons butter and blend in flour. Add evaporated milk and 3/4 cup water from cabbage. Cook and stir constantly until thickened and flour is cooked. Add salt to taste. Place layer of cabbage in buttered casserole dish. Pour part of the sauce over it and sprinkle with part of cheese. Repeat layers until all is used up. Sprinkle with crumbs mixed with remaining 3 tablespoons melted butter. Bake for 20 minutes until nicely browned.