There are numerous ways of preserving Chestnuts; this is mine.
With a very sharp knife, I cut a cross into the pointy end of each Chestnut.
Boil for between 15 and 20 mins, until semi-open.
Peel away the outer shell (don't worry too much about the inner skin, just remove as much as possible), and remove the nut.
Then when cool place in freezer bags, and freeze. Couldn't be simpler.
These are semi-cooked Chestnuts which can later be roasted, or used in blitzed soups, or even puréed for sickly sweet desserts (not my thing).
As with all freezing, only PERFECT produce should be used.
It's now the end of the Chestnut season, so this may be your last chance to preserve. Don't buy them later-on towards Christmas as 'fresh'; they won't be, and will probably contain worms.
I put away 3 bags from the above, and now have a total of about 12 bags awaiting Winter; that's plenty for me!