Peel and chop the potatoes. Place in a pot of salted cold water and bring to the boil. Simmer for 10 minutes before taking off the heat and draining well. Shake the par cooked potatoes in the pot to fluff them up, giving the potatoes plenty of edges to be crisped up once cooked.
Heat a generous layer of duck fat in an oven dish big enough for the potatoes to fit in one layer.
When the fat is hot add the potatoes and bake for 45-60 minutes, turning a couple of times so they are crisp all over.