Rinse the 2 cups short-grain Japanese sushi rice uncooked in a sieve or mixing bowl under cold water, gently swirling with your hand, until the water runs mostly clear — about 3–4 rinses. Drain well. This removes excess starch and is essential for fluffy, non-gummy rice.

Combine the rinsed 2 cups short-grain Japanese sushi rice uncooked and 2½ cups of water in a saucepan. Bring to a boil over high heat, then immediately reduce to the lowest heat setting, cover tightly with a lid, and cook for 15 minutes. Do not lift the lid during cooking.

Remove the saucepan from heat and let the 2 cups short-grain Japanese sushi rice uncooked steam, still covered, for 10 minutes. This allows the rice to finish cooking evenly in residual steam.

While the 2 cups short-grain Japanese sushi rice uncooked steams, combine the 3 tbsp rice vinegar, 2 tbsp granulated sugar, and 1 tsp kosher salt in a mixing bowl. Stir until the sugar and salt are fully dissolved. (You can microwave it for 15 seconds to help it dissolve faster.)

Transfer the cooked 2 cups short-grain Japanese sushi rice uncooked to a large mixing bowl (ideally a wide, shallow wooden or glass bowl). Pour the vinegar mixture evenly over the 2 cups short-grain Japanese sushi rice uncooked. Using a spatula or flat spatula, fold and cut the 2 cups short-grain Japanese sushi rice uncooked gently — do not stir in circles, as this will make the rice gummy. Fan the 2 cups short-grain Japanese sushi rice uncooked as you fold to cool it quickly. Season to taste. The rice should be glossy, slightly sticky, and just barely warm before rolling.

In a mixing bowl, mix the shredded 8 oz imitation crab sticks shredded or sliced into thin strips with the 3 tbsp mayonnaise Japanese mayo (Kewpie) preferred until evenly coated. Slice the 2 whole ripe avocado peeled into thin strips and cut the 1 whole English cucumber peeled into thin matchsticks. Keep all filling components ready at your workstation.

Wrap your bamboo steamer sushi mat tightly in plastic wrap (this prevents rice from sticking to it, since California rolls are inside-out — rice on the outside). Mix 1 cup of water with 1 tbsp 3 tbsp rice vinegar in a mixing bowl for wetting your hands.

Place a sheet of whole nori sheets full-size, shiny side down, on the plastic-wrapped mat. Wet your hands with the vinegar water. Grab a generous handful of short-grain Japanese sushi rice uncooked (about ¾ cup) and spread it in an even layer across the entire 4 whole nori sheets full-size sheet, pressing gently to the edges. The layer should be thin — about ¼ inch thick. Re-wet your hands as needed to prevent sticking.

Sprinkle 3 tbsp toasted sesame seeds white evenly over the 2 cups short-grain Japanese sushi rice uncooked layer. Then, carefully flip the 4 whole nori sheets full-size sheet over so the rice side faces down onto the mat and the bare nori side faces up.

Arrange the fillings horizontally across the lower third of the whole nori sheets full-size: a line of the imitation crab sticks shredded or sliced into thin strips-3 tbsp mayonnaise Japanese mayo (Kewpie) preferred mixture, a few whole ripe avocado peeled strips, and a row of whole English cucumber peeled matchsticks. Don't overfill — a thin, even layer of each works best.

Lift the edge of the mat closest to you and roll it over the filling, tucking firmly and evenly as you go. Apply gentle, even pressure with your fingers through the mat to shape the roll into a tight cylinder. Continue rolling forward until the roll is sealed. Give it one final firm press and shape with the mat.

Using a sharp knife, wet the blade with the vinegar water (this prevents sticking). Slice the roll in half first, then line the two halves up and cut each into 4 equal pieces — giving you 8 pieces per roll. Wipe and re-wet the knife between each cut for clean slices.

Repeat steps 8–12 with the remaining whole nori sheets full-size sheets, 2 cups short-grain Japanese sushi rice uncooked, and filling to make 4 rolls total (32 pieces). Arrange the pieces cut-side up on a serving platter.

Serve immediately with 4 tbsp soy sauce for serving for dipping, and 2 tbsp pickled ginger for serving and 2 tbsp wasabi paste for serving on the side if desired. California rolls are best enjoyed fresh, within 1–2 hours of rolling.