Source: chef Shawn Dempsey, Chiso, at Cook’s World cooking class

3 cups short grain japanese rice (1 cup is about 3-4 rolls)
3 1/4 c. water
Vinegar:
1/3 c. rice vinegar
3 tbsp sugar
1 tsp salt

Wash rice with cold water until water is clear (can soak for 30 minutes before cooking). Add a little over 1 cup of water to 1 cup of rice (or 1 knuckle over the rice). Keep the lid on the rice, or cover with foil with a little hole in it. Cook on high heat until it boils, then turn down to low, simmer 10 minutes. Turn the heat off, let it sit for 10 minutes, do not remove the lid ever.

Transfer to a big mixing bowl or deep plate, spread out evenly, add vinegar mixture, fold in with spatula, cool it with a fan or an open window, let it cool.
10 minutes later, turn it over so it all cools at the same rate. After 15-20 minutes, it’ll be ready to use.