Rinse the rice in a sieve until the water runs clear. This usually takes several minutes. Drain well, then place in a medium saucepan and cover with 260ml cold water. Add the nori, if using.
Let the rice soak in the water for about 5 or 10 minutes, then cover with saucepan lid and bring to the boil. You will know it has started to boil when the lid shakes - don't be tempted to lift the lid. Instead, lower the heat to low and cook for a further 5 minutes.
Remove the pot from the hob and let stand for at least another 10 minutes - with the lid still on.
Fluff the cooked rice with a fork to break up any lumps, the allow to cool for using in sushi.