In a bowl, wash uncooked Japanese short-grain rice. In a bowl, submerge the rice in water and, using your hands, swirl the rice in one direction 10-15 times. Then drain the water. Repeat this step 4-5 times, with the water getting clearer each round.
Then drain all the water and put rice in donabe or pot.
To prepare the sweet potato, thoroughly wash the outside so there is no dirt or grime on the skin. This is important as we are using the whole sweet potato.
Once it is clean, slice the sweet potato in 2cm thickness. You will end up with a circle. Then, cut the circle in quarters. You will end up with a quarter of a circle.
Submerge the sweet potato in water. This will remove the starch from the sweet potato and will help with any discoloration it may develop.
Then drain the water from the sweet potato and add the sweet potato to the donabe.
Add mirin, sake, salt, water to the donabe
Turn on the heat to medium and cook for 15 minutes. It should be boiling and steaming.
Turn off the heat and let it rest for 20 minutes. Do not open the lid or touch the rice at this point.
After 20 minutes, open the lid and mix the rice from bottom to top.
Serve in a chawan or rice bowl, sprinkle goma or sesame seeds and enjoy!