Prepare the riceRinse the rice in a pot under running water three to four times. Add water and let the rice soak for thirty minutes.
Prepare the Sweet Potato: Dice the sweet potato and soak it in water for five minutes, then drain.
Simmer: Drain the rice, add fresh water, and cook over medium heat. Stir in the sake and salt. Add the diced sweet potato to the rice. Cover and simmer on low heat for ten minutes.
Rest: Turn off the heat and let the rice sit, covered, for ten minutes.
Fluff: Open the lid and gently fluff the rice with a rice paddle or big spoon.
Notes
Storage: Wrap one serving in plastic wrap and freeze it. It will last up to one month.
Soaking sweet potatoes can remove the bitterness and prevent the color from changing or darkening.
Japanese sweet potato skins are edible and nutritious, like other varieties. I recommend eating them with the skin on, but you can peel it off if you prefer.