Preheat grill using two zone method with lump charcoal or embers from a wood fire in a fire pit.
Score the flat side of the chestnut shell with a sharp paring knife.
In a large cast iron pan, distribute the chestnuts with the scored side facing up, taking care not to overcrowd the pan. Typically 1 pound of chestnuts are cooked in two waves.
Place the pan over the hot coals or embers. Leave the pan for 5 - 7 minutes or until a slight nutty aroma comes from the nuts. Some small smoking may occur and is normal.
Stir the nuts and allow to continue roasting in the pan for an additional 5 - 7 minutes. no need to move the pan.
Remove the pan from the coals using welding gloves (pan will be HOT) and put roasted chestnuts in a serving dish. Repeat for additional batches.
Serve warm with a dash of Maldon finishing salt.
Notes
If using a grill grate, allow for a little more time to the roasting process since the pan won't be in direct contact with the hot coals.