If you prefer to roast fresh chestnuts instead of using vacuum-packed ones, cut a slit in the shell of each chestnut with a serrated knife. Roast the chestnuts in a cast iron skillet in a 400? oven for 20 minutes or until tender. Peel them as soon as they are cool enough to handle. If you have difficulty peeling them, reheat them for 5 minutes to further loosen their skins.