Find the flat side of each chestnut and cut a large X through the shiny brown outer shell. This lets steam escape and prevents the chestnuts from exploding. (If the cut is deep enough it also makes peeling off the shells easier).
Arrange chestnuts on a baking sheet or in a shallow pan, with the cut sides up.
Roast in oven for 15 to 25 minutes, or until chestnuts are tender and easy to peel.
Peel roasted chestnuts as soon as they are cool enough to handle. Once they cool completely, they are difficult to peel. Be sure to peel away both the outer shell and the bitter inner husk.
