Stand each chestnut on its base and grasp firmly with your left thumb and forefinger.
With a small sharp pointed knife, cut a slit down, preferably, the flat side (if there is a flat side) of the chestnut. Be careful! The slit should cut all the way through the shell. This is the safest way to make the slit, but, the most functional slit is across the top of the nut. This slit makes it easiest to pry the shell open and pop out the nut, after baking.
Preheat oven to 425 deg (400 if convection oven).
Roast for 20 mins.When nuts are cool enough to handle, pull the shell apart and the nuts should fall right out, leaving the shell and the brown membrane behind.