1) Place a pot full of water over high heat and bring to a boil.
Fill a large bowl with cold water and place a strainer in it. Add the rice and wash well for 2-3 minutes.
Transfer to a bowl and add the water, rice vinegar, mirin, and sugar. Mix with a spoon.
Cover with plastic wrap and place over the pot of boiling water (bain-marie)
Cook for 30 minutes.
Remove the bowl from the bain-marie. Take the plastic wrap off. Mix with a spoon and set aside until it is completely cool.