In this simple shepherd’s pie recipe, we call for flavorful lean ground lamb, which isn’t always easy to find. You can use lean ground beef or turkey instead. If you want to use lamb, ask your butcher to grind it for you or, to make your own ground lamb, start with a lean cut of lamb, such as leg or loin, trimmed of any excess fat and cut into 3/4-inch pieces. Pulse briefly in a food processor just until uniformly ground.