To make homemade vinegar: Boil 3 tablespoons rice vinegar and 3 tablespoons sugar with a pinch of salt. Stir until the sugar has melted. Remove from the heat and leave aside to cool completely.
Rinse sushi rice until clean then soak it in water for 25-30 minutes. Drain the rice and add water and bring to a boil.
Cover and simmer over a very low heat for 15 minutes, then allow a standing time of another 15 minutes.
Put the cooked rice at room temperature in a basin and drizzle in the sushi vinegar or your homemade vinegar.
Mix the rice and sushi vinegar with a rice paddle or a wooden spoon.
Cool the rice slightly by fanning it with a piece of cardboard while fluffing up rice from bottom up with the rice paddle. Use the rice immediately or cover with a damp tea towel to retain moisture and use within an hour or two.
The rice grains should be properly mixed with the sushi vinegar to prevent it from becoming lumpy and pasty.