Using a sharp paring knife, make a slit on the rounded side of each chestnut. Cook's Note: The slit will prevent the chestnuts from exploding while cooking. Place the chestnuts on a perforated pan and roast over a fire for 10 to 15 minutes. Alternatively cook in a preheated oven at 400 degrees F for 15 to 20 minutes. Peel the charred shell and serve.