To make the rice, rinse it in several changes of water until the water becomes clear, then drain really well. Put the rice in a pan, add 250ml cold water and bring to the boil on a high heat. Cover tightly, then simmer on a low heat for 30 minutes. Remove from the heat and leave covered for 15 minutes to allow it to steam.
Meanwhile, put the rice vinegar, sugar and 1 tsp salt in a saucepan. Heat until the sugar dissolves, then take off the heat and cool to room temperature. Put the still-hot rice in a very large shallow bowl and add ¼ of the rice seasoning. Fold in then repeat 3 times until all the seasoning is used up. You can help cool the rice down by fanning it for 5 minutes.