Preheat your oven to 400°F (205°C). Use a sharp knife to make a small, shallow X on the flat side of each chestnut. Place the chestnuts in a single layer on a baking sheet. Roast the chestnuts for 15-20 minutes, depending on their size. Remove the chestnuts from the oven and allow them to cool for a few minutes. Once the chestnuts are cool enough to handle, use a paring knife or your fingers to peel off the outer shell and the thin, papery skin underneath. Now they're ready to use for this chestnut chicken recipe.