2kg floury potatoes (desiree, king edward), peeled, cut into chunks
200g duck fat
Sea-salt flakes and freshly ground black pepper, to season
Put potatoes in a large saucepan and cover with cold salted water. Bring to boil over high heat. Reduce heat to low and simmer for 2-3 minutes until slightly tender. Drain, return to pan and give a good shake to rough up. Tip into a large baking dish lined with baking paper and chill, uncovered, overnight (or cool thoroughly if your time is short).
Preheat oven to 180 degrees C fan-forced (200 degrees C conventional). Put duck fat in a large baking dish and heat in oven. After 10 minutes, transfer cold potatoes to hot duck fat – you should hear them sizzle as they hit the fat. Toss to coat in fat and season well, then spread in a single layer. Roast for 1½ hours, turning once and basting with fat to evenly brown. Serve immediately.