With the flat side of the chestnut down, make a straight slit across the top through to the meat, using a serrated knife - do not make an X

Place chestnuts into a saucepan of cold water, enough to cover

Salt the water and bring to a simmer, simmer for a minute or two then remove chestnuts from water

Place chestnuts in oven-proof pan and cook for 15 minutes at 425°F / 220°C

Remove from oven and place a towel over them to steam for 15 minutes