Spread one quarter of the potatoes at the bottom of a 20-cm (8-inch) square Pyrex pan. Layer with one third of the sausage slices. Continue with the remaining potatoes and sausage, alternately. Drizzle with the cream. Bake for about 1 hour and 45 minutes or until the potatoes are tender. Cover and let stand for 15 minutes before serving; the gratin will be easier to cut.