Put the sliced potatoes in a large saucepan, cover with cold water, add the salt and bring to the boil. Drain.
Meanwhile, put the butter in a large, shallow, ovenproof dish or roasting pan, take 1–2 tablespoons of the fat from the turkey, add it to the butter and heat it in the oven, above the turkey, until it is sizzling hot. Add the potatoes to the hot fat and turn until evenly coated. Cook on the shelf above the turkey for 1–1 1/2 hours, or until crisp and golden brown. If you have a double oven, it may be easier to bake the potatoes separately in the second oven, preheated to 180°C.