Preheat the oven or airfryer 356F / 180C, unless you are using a pan on the stovetop.
Oven - cook chestnuts on a lined baking sheet. Shake baking sheet halfway through cooking. Depending on your oven, you may need to flip the chestnuts so they cook evenly. (Approximately 30 minutes).
Air Fryer - shake basket to flip chestnuts a couple of times during cooking. (Approximately 30 minutes).
Pan - Roast over a medium-low flame, tossing often. (Approximately 10-15 minutes).