Using a thin, sharp knife, make slices three quarters of the way through each potato. Try to get them as close together as possible (about 2-3mm) and make sure you don't cut all the way through.
Mix together the oil, garlic powder, salt and pepper.
Brush the potatoes all over with the oil mixture.
Place the potatoes into the air fryer.
Cook at 180°C/350℉ for 20 minutes, turning halfway through.
Notes
There is no need to spray the basket with oil first, as these potatoes won't stick to the basket because they are coated in oil.
You can cut the slices as thick or as thin as you like, but if they are thick they won't get very crispy.
Cooking times will vary, so you might need an extra couple of minutes to get these air fryer hasselback potatoes crispy.
Whether you peel the potatoes or not is a total preference thing. We like how crispy the skin gets, and there is also lots of nutrition in it.
Make sure you don't overcrowd the air fryer basket, otherwise your potatoes won't get crispy.