Preheat the oven to 220C.
Put the potatoes in a pan of cold, salted water. Bring to the boil and cook until just tender – about 10 minutes.
Drain and return to the pan. Put the lid on and shake the pan well to rough up the edges of the potatoes – this will give them a nice crispy outside.
Put the fat in a large roasting tray and place in the oven to heat up. When it;s smoking hot, add the potatoes.
Toss well in the fat so they are completely coated.
Roast for 50-60 minutes, turning 2 or 3 times to ensure they are evenly browned and golden.