Make your ingredients in amounts according to how much roast beef and gravy you have left over. Layer in a casserole, again depending on the amount of ingredients:

- sliced onion
- a layer of potatoes, sliced crosswise
resembling a potato chip, 1/4" thick
- a layer of sliced roast beef

Season each layer (on top of potatoes) with salt and pepper to taste. Dilute leftover gravy with water and pour over entire casserole. Cover with a lid and bake at 350 degrees for about 40
minutes or until knife will pierce potatoes easily. Remove cover (or foil) and continue to bake for about 10 minutes.