Soak whole chestnuts in water for at least 1 hour, or in warm water at around 120℉ (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. Repeat this process several times, changing the water each time.
Soak the rinsed rice in water (as specified in the ingredient list) 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 cook 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.