Photograph: Maja Smend
Preheat the oven to 200°C, fan 180°C, gas 6. Put the potatoes in a pan of salted water. Cover and bring to the boil. Simmer for 10 minutes – they should still feel firm; drain.
Divide the oil or goose fat between 2 roasting tins; preheat until sizzling. Add the potatoes, sprinkle with sea salt and turn them in the oil to coat.
Roast the potatoes for 1 hour until golden. Turn them halfway; sprinkle with sesame seeds.
Get ahead: prepare up to the end of step 1 a few hours ahead.