1) Pre heat the oven to 170C gas 3 2) Heat the oil in a large frying pan, add the lamb and fry over a high heat until browned on both sides. 3) Lift out with a draining spoon and transfer to the base of an oven proof casserole dish. 4) Add the onion to the pan and fry, stirring, for 5 minutes or until lightly browned. 5) Add the mushrooms and cook for 2 minutes more. 6) Stir in the flour, then gradually mix in the stock and port. 7) Add the tomato purée, cranberry sauce and dried cranberries and season to taste. 8) Bring to the boil, stirring then pour the hot sauce over the lamb. 9) Arrange the sliced potatoes on top, overlapping the slices in two layers. 10) Gently press the potatoes down into the sauce and cover. 11) Cook in the oven for 1½ - 2 hours until the lamb is cooked. 12) Remove the lid ½ hour before the end of cooking time if you want to brown and crisp the potatoes.