Shepherd's pie is all about leftovers. Also known as cottage pie, it's a combination of what's sitting in your fridge, namely roasted meat and veggies, which you mix and spread into a pie dish lined with mashed potatoes. Freshly mashed potatoes or leftover smashed spuds work equally well. Once the dish is full, the entire top of the pie is covered with additional mashed potatoes, then baked.
Shepherd's pie began as an English dish, and lamb or mutton was the traditional meat used. In America, beef is more common. This is a great meal to dress up any way you'd like. Add zesty spices or more exotic veggies, or brush the top of the pie with a beaten egg for a little golden glaze. Omit the meat altogether to make a vegetarian meal.