Place chestnuts in a colander and rinse under cold running water. Drain.
Place the flat side of the chestnut down on a cutting board, making sure that the rounded side (aka the belly side) is facing up. Hold the chestnut firmly and cut horizontally across the rounded side using a sharp paring knife (or a chestnut knife, if you have one.) Then, turn the chestnut 90 degrees and make a second cut, forming an X. As you are cutting, do your best not to score the inner skin. Continue with the rest of the chestnuts.
Transfer the now-cut chestnuts into a bowl. Cover it with cold tap water and let them sit for 30 minutes to an hour.
Preheat your air fryer to 350 °F.
Drain chestnuts and transfer them onto a clean kitchen towel. Dry them off as much as you can.
Place them in the air fryer basket, making sure that the cut side is facing up. Do not overcrowd the basket. If needed, you can bake it in two batches.
Air fry them for 17 minutes, shaking the basket halfway through the air-roasting process.
Once the air frying is completed, transfer the now-very hot chestnuts onto a clean kitchen towel. Collect the edges of the cloth in the middle and turn it into a small pouch. Let them steam in the “pouch” for 5 minutes or so. Alternatively, you can use a paper bag to do this. Simply place the hot roasted chestnuts in it, roll the bag to trap the steam inside, and let it steam for 5 minutes.
Holding the pouch in your hand, give it a gentle squeeze to loosen the shells. Then, carefully remove the outer shell of the chestnuts when they are still hot by gently pulling back on the scored “X,” peeling away the papery skin and exposing the yellow flesh inside. If you are unable to remove the fuzzy inner skin by hand, use a small sharp knife to peel it, being careful not to pierce the yellow nut inside.
Enjoy while still warm.