Rinse the short-grain Japanese rice 5 times under cold water to remove excess starch.

Drain the rinsed rice in a colander and let it dry for 15 minutes.

Cook the rice in a rice cooker according to the manufacturer's instructions, or in a saucepan.

If using a saucepan, combine the rice with 2 cups of cold water in a medium saucepan.

Bring the mixture to a boil over high heat.

Once boiling, cover the saucepan tightly and reduce the heat to moderate.

Cook the rice for 10 minutes over moderate heat.

Reduce the heat to low and cook for another 10 minutes.

Remove the saucepan from the heat and let it stand, covered, for 15 minutes to steam.

While the rice is cooking, prepare the seasoned vinegar.

In a small saucepan, combine sake-mash vinegar (or white wine vinegar), rice vinegar, sugar, and salt.

Warm the mixture over moderate heat, stirring until the sugar and salt are completely dissolved.

Once the rice is cooked, transfer it to a very large bowl.

Sprinkle 1/2 cup of the seasoned vinegar evenly over the rice.

Use a spatula to gently slice and separate the rice grains while mixing in the seasoning, avoiding mashing the rice.

Fan the rice while mixing it to help it dry and cool slightly.

Wipe down any stray grains from the sides of the bowl.

Cover the seasoned sushi rice with a damp towel to keep it warm and prevent it from drying out until ready to use.