A "common" holiday tradition
Although "chestnuts roasting on an open fire" sounds like an image reserved for a special occasion, it is interesting to note that in Europe, Asia, and Africa, they are a common substitute for potatoes when a starch is needed in a dish. That is perhaps where the Christmas tradition came from when we think of Europe in particular; a family gathered around a hearth in the winter would toast chestnuts to fill the air with the smoky scent and banish the cold.
How to enjoy them
Our chestnuts are, of course, raw, and separated from the spiky outer husk. You should always blanch or cook fresh chestnuts in order to remove the shell and skin. Do not eat raw chestnuts, as they have high levels of tannic acid (a basic chemical used in the staining of wood). Instead, take a sharp knife, and mark an "x" on the flat side of the chestnut. You can then boil them for about three minutes, and peel off the skin and shell a few of them at a time. The chestnuts are now safe to eat.
Roasting Chestnuts
If you want to roast them, make the cuts into the nuts as you would for boiling. Failing to do this may result in the chestnuts exploding. Roast them for 15-20 minutes in a 400 degree oven. If you decide to skip the oven and use the more old-fashioned method of roasting—over the fire-use an aluminum pie plate with rows of holes punched into it to roast the nuts. Be sure to puncture the chestnuts as well, in order to release steam.
Even if you don't have the open fire for the chestnuts, it will still feel a little more festive to have them at your holiday celebration. Gather the family around to eat them as a snack before the big meal.