Rinse the rice in a fine-mesh strainer until the water runs clear.
Combine the rinsed rice, water and Kombu (if using) in a medium saucepan. Let soak for 30 minutes.
Bring the rice to a boil over high heat, then reduce to low, cover, and simmer for 15 minutes.
Remove from heat and let stand, covered, for 10 minutes.
While the rice cooks, combine rice vinegar, sugar, salt, and soy sauce in a small saucepan. Heat gently, stirring until sugar dissolves. Remove from heat and cool to room temperature.
Transfer the cooked rice to a large, wide non-metallic bowl and remove the kombu.
Drizzle the vinegar mixture over the rice. Use a rice paddle or wooden spoon to gently fold and cut through the rice, being careful not to mash the grains.
Sprinkle the crumbled nori over the rice and continue folding gently.
Gently mix the rice as it cools to room temperature. Cover with a damp cloth until ready to use for sushi or as desired.
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Notes
Long-grain rice won’t give you the right texture for sushi, so make sure to stick with short-grain for the best results.Make sure to rinse the rice really well until the water runs clear. This gets rid of extra starch and helps keep the rice from getting too sticky or gummy when it cooks, so the grains stay separate.Refrigerate any leftovers in an airtight container for up to 5 days.