Soak whole chestnuts in water for at least 1 hour, or in warm water at around 122℉ (50℃) for 20 minutes.
Cut off the bottom part of the chestnuts and peel the outer shells.
Remove the inner skins from the chestnuts thoroughly with a knife. Fill a bowl with water and place the peeled chestnuts in it. Soak them for 30 minutes, changing the water when it becomes cloudy.
Place a sieve over a bowl, add rice, and rinse it with water (not included in the recipe). Repeat this process several times, changing the water each time.
Soak the rinsed rice in water (as specified in the recipe) in a pot for at least 30 minutes.
Add sake and salt to the pot and mix. Cut the chestnuts into bite-sized pieces and place them evenly on top of the rice.
Cover the pot and bring it to a boil. Once boiling, reduce the heat to low and continue cooking for 10 minutes, or slightly longer for larger quantities (11 minutes for 4 servings, 12 minutes for 6 servings).
Turn off the heat and let it steam for 15 minutes with the lid still on.