Slice them thinly. (If you have a mandoline, here's a great reason to use it -- feel free to try your ruffle blade!)
Place in a large pot of cold water to soak for a few minutes. (The soaking both protects the potato slices from discolouring in the air, and leeches starch out, making for a crispier chip.) Swirl around a bit if you feel like it.
Pop the duck fat in the Actifry and heat for 2 minutes.
Drain the potato slices well; then pat dry in tea towel, or swirl in a salad spinner.
Add to Actifry bowl, spreading them out.
Cook for 40 to 50 minutes, at 10 minute intervals. At the end of each interval, use tongs to break up any clump and spread them out again.
Transfer to a bowl, toss with a few pinches of Maldon Salt (or gourmet salt or salt substitute of your choice.) Serve hot or warm.