Cut and soak the potatoes
Scrub the potatoes thoroughly, then slice them lengthways into fries approximately 6–12mm thick. Place them in a bowl of ice water and soak for at least 1 hour. For advance preparation, they can be refrigerated in the water for up to 24 hours.
Preheat the air fryer
Preheat the air fryer to 200°C for about 15 minutes.
Dry and season
Drain the potatoes and spread them over a clean tea towel or kitchen paper. Pat them completely dry, transfer them to a bowl and toss with the oil, thyme, salt and black pepper until evenly coated.
Cook the first side
Arrange the potatoes as evenly as possible in the air fryer basket. Air fry at 200°C for 10 minutes.
Toss and finish cooking
Pull out the basket and toss the fries so that they cook evenly. Return them to the air fryer for another 10–12 minutes, removing any pieces that brown too quickly, until the fries look dry, golden and crisp.
Cool and serve
Transfer the fries to a serving bowl and leave them for a few minutes so the exterior can become crisper. Taste and add extra thyme, salt or black pepper as desired before serving.