Weigh out the potatoes. For 4 people, you want about 1 kg (2 pounds / 7 medium-sized potatoes.) You can use a bit more potato if you wish -- up to 50% without necessarily needing more duck fat.
Peel the potatoes. Pop them into a bowl of water for 30 minutes to 1 hour (more is fine). This helps to leech starch out of them, which results in a crisper product at the end. If you don't have time to let them stand in water to soak, at least give them a quick swirl in a pot or basin of water or a quick rinse under the tap. Then, before proceeding, dry in a salad spinner or pat dry in a tea towel. That's another secret to good roast potatoes, is getting moisture out of the roasting environment because you don't want them to steam.
Cut the potatoes into chunks about 5 cm (2 inches) in size.
ACTIFRY: Put 1 tablespoon of duck fat into the Actifry; heat it for 2 minutes. Add the chunked potato. BASKET: Melt 1 tablespoon of duck fat in microwave in a microwave-safe jug. Toss potatoes in melted fat in a large bowl. Put into air fryer basket.
Cook for 30 minutes. (Note: to be clear, yes, you leave the paddle in for the entire cooking.) Check the potatoes gently with a fork for doneness inside, and check them visually for an appealing golden colour. Feel free to give them another 5 or 10 minutes if they need it to get nice and crispy. Serve piping hot.
For some reason, leftover roasted potatoes never seem to reheat as good as when freshly made, so you're best to make just as much as you need. If you do need to reheat leftover roasted potatoes, a few minutes in the air fryer is the best way to do it.