This easy pie is an excellent way to use leftover roast beef or pork. For the biscuits, use refrigerated biscuits, frozen, or homemade. The dish is made with homemade gravy, but in a pinch, you could use a jar of gravy or 2 cups of gravy made from a dry mix. Cooked green beans, mixed vegetables, or diced cooked corn or carrots are all excellent choices for vegetables in the filling.