While oven is heating, use a sharp, pointed knife to make a horizontal slice or an “X” in the skin of each chestnut. (This is an essential step that prevents the chestnuts from exploding.)
Arrange sliced chestnuts on a baking sheet with the flat side down and the sliced side facing up.
Roast in middle rack of oven for 15-20 minutes. Return occasionally to shake pan.
Remove from oven and let cool until chestnuts are still warm, but no longer hot to touch.
