Wash the potatoes. Peel or not according to your own preferences. Put through a chipper or cut manually into chips.
Paddle-type fryer (such as Actifry™): Put the chipped potato into the chip pan, with the 1 teaspoon of duck fat. Cook for 30 minutes.
Basket-type fryer (such as Philips AirFryer™): Put the duck fat in a medium-sized microwave-safe bowl, zap it for about 10 to 15 seconds, then toss the cut potato in it till coated. Cook for 20 to 25 minutes, starting at 160 C (320 F). Half-way through, toss, and raise temperature to 180 C (350 F).
If you double the recipe, allow about 10 minutes extra cooking time in an Actifry.