Place the potatoes in a pan of cold water and bring to the boil, then simmer for 10 minutes to parboil, until they are just beginning to fall apart. Drain and allow to cool for 10 minutes.
Meanwhile, place the goose fat in a roasting tin in the oven. Once hot, carefully toss the potatoes in the fat. Roast for about 45 minutes, or until nice and crispy.