Right! Earthbabe's just reminded me of Richard Mabey (under sweetchestnuts), so this is what he has to say on the matter:

Chestnut puree (doesn't mention preserving this, but I would hazard a guess that it can happily be frozen in it's pureed state.)

Shell and peel the chestnuts and boil them in a thin stock for about 40 mins. Strain off the liquid and then rub the nuts through a sieve or process them in a liquidiser. The resulting puree can be seasoned and used as substitue for potatoes, or form the basis of stuffings, soups and sweets, such as chestnut fool.

Chestnut flour.

Store in a warm, dry, well-ventilated room for a couple of months (!). they must be individually shelled and ground as finely as possible. The flour is fragrant and excellent in cakes and breads, but can be reluctatn to rise and is probably best mixed with an equal amount of ordinary wheat flour.

I guess you could also use them in a variety of dishes which could be frozen ahead, such as nut loaf, or brussels and chestnuts etc.