Who could have imagined that the classic corned beef deli sandwich could be eaten any other way than as a sandwich? But, the ingredients of this grilled sandwich actually lend themselves to a delicious casserolethe corned beef, sauerkraut, and cheese are layered with thousand island dressing, then topped with buttered rye bread crumbs. It's an excellent way to use leftover corned beef, especially for reuben sandwich lovers. Use leftover corned beef, deli corned beef, or canned corned beef in the recipe. If you use canned corned beef, chill it in the can for a few hours so it will be firm enough to dice.