So how exactly do you go about cracking this particular nut?
First, using the tip of a sharp paring knife, score an X on the flat side of the chestnut. Place scored chestnuts on a baking sheet and roast in a 425 degree oven for 15 minutes. This will cause the X to open up a little. If you actually want roasted chestnuts (rather than simply roasting them for peeling the skin), keep them in the oven for another 20 minutes, or until they are tender. While the chestnuts are still hot, peel the shell, then remove the papery skin. Once they cool, the shells are difficult to remove, so keep the batch warm while you work.
Finally, if the thought of wielding a sharp paring knife on a hard slippery shell concerns you, and you have a particular love of chestnuts, you might want to invest in a handy little gadget that will mark a perfect X. Looking much like a garlic press, the Chestnutter takes the work (and anxiety) out of shelling dozens of chestnuts, and more importantly, leaves your fingers intact.