A critical step is making great sushi rice: seasoning it as Morimoto does, with a mixture of rice vinegars, sugar and salt, then carefully separating and fluffing the grains with a slicing motion. “Use your fingertips to delicately spread the rice,” says Morimoto. “You want a little space between the rice grains so that they remain fluffy.”
Step 2: Prepare the Fillings
To be eaten safely, sushi-grade fish must be handled correctly: It should be frozen for at least one day to kill any parasites. For the best flavor and texture in oily, strong-smelling fresh fish, such as salmon and mackerel, rub the fillets with fine sea salt and let stand for 30 minutes; rinse the fish well, pat dry and sprinkle all over with rice vinegar.
Crab Meat from Dungeness, blue or king crabs is best. Pick over the meat for bits of shell.
Tuna If a piece of tuna is sinewy, simply scrape the meat off the sinews with a sharp knife.
Salmon Slice salmon across the grain into strips about 4 inches long and 1/4 inch thick.
Cucumber Seed a cucumber, then slice it—including some of the skin—into a thin julienne.
Avocado Cut a ripe Hass avocado in half. Carefully strike the pit with the blade of a heavy chef’s knife, then twist the knife to remove the pit. Peel the halves, then cut them into 1/4-inch-thick slices.
Step 3: Form the Maki
Carefully wave a 4-by-7 1/2-inch sheet of nori over an open flame until crisp and fragrant, then transfer to a bamboo mat. Wet your hands in water that’s seasoned with rice vinegar, then scoop up 1/2 cup of sushi rice. Gently form the rice into a loosely packed, palm-width log. Place the log at one edge of the nori and begin spreading it across to the other side.
Add the Wasabi and Filling
Continue to spread the rice all over the nori, rewetting your hands as necessary, until an even layer covers all but a 1/4-inch border at the top edge. Spread about 1/4 teaspoon of wasabi lengthwise along the middle of the rice. Lay about 2 ounces of the filling (either a single ingredient or a combination) along the center of the rice.
Wasabi Tip: “Rice, wasabi and fish should be in harmony,” says Masaharu Morimoto. “We use more wasabi with fatty fish, less with lean fish.”
Step 4: Roll the Maki
Roll the bamboo mat up and away from you, curling the nori and rice around the filling; use your fingers to hold the filling in place as you roll. Secure the roll with the 1/4-inch flap of nori. Once the roll is sealed, gently squeeze, pressing gently on the top and sides, to compress the roll slightly and form a rough square shape. Press on each end of the roll to make a neat surface.
Step 5: Cut the Maki
Lift the roll off the bamboo mat and transfer it to a work surface. Dip the tip of a long, sharp knife into vinegar water; let the water run down the length of the blade. Using a long slicing motion, cut the maki in half, then cut each half into thirds to form six even pieces, rewetting the blade as needed. Serve.