When cooking tougher or fattier cuts of lamb, that benefit from slow cooking, it is always advisable to cover the lamb with foil to stop it from drying out. For larger joints, such as slow cooked lamb shoulder, you can remove the foil towards the end of cooking to allow the meat to brown. It is not essential to roast lamb shanks in foil if you are cooking them in liquid, as the pan lid will protect the meat.