Place the piece of pork, basted with lard, salt and pepper, in a well-greased pan. Surround it with the potatoes, add the garlic cloves and sage. Put it in a preheated oven at 200°C/400°F. Turn the meat every now and then and moisten it with the cooking juices. After half an hour remove the potatoes and leave the meat to cook for about another half an hour. Arrange the pork on an oval serving plate with the potatoes and garlic. Peel the rennet apples and cut them into pieces. Let them soften in a pan with the sugar, salt, cinnamon and the sage.
Serve with a rennet apple sauce spiced with cinnamon.