Take one chestnut at a time on a cutting board. Place them on the board the flat side down, hold firmly between your fingers, and with a sharp paring knife, cut a long slit from side to side.
Put the cut chestnuts into the water bowl. Let them soak at least for an hour.
Once the chestnuts has soaked enough, preheat the oven to 350 F / 180 C.
Drain the soaked chestnuts and dry them with a kitchen towel.
Line an oven tray with non-stick baking paper.
Arrange the chestnuts on the tray the cut side up. The nuts have to fit on the pan in one layer.
Roast the nuts for about 25 minutes.
Tips
The nutrition values are a pretty exact for 100 grams of chestnuts.