Masaba Oshizushi

1. Lay out rice in a line that roughly equals the size of the mackerel fillet you have, place a sheet of plastic wrap over top and use your hands to press it into a log. Remove the plastic, take the fillet and lay it on top of the rice. Place the plastic wrap over top and hand press the mackerel fillet over the rice to form a rough box shape. You can use the kombu sheet or a bamboo mat at this point to assist in evenly shaping the rice. Wet the tip of your knife to prevent sticking and slice the roll into 8 to 10 slices, then remove the plastic wrap. Serve with soy sauce.

Sushi Rice:

1. Combine the vinegar, sugar and salt in a small saucepan. Heat over high heat, stirring, until the sugar and salt are dissolved. Set aside to cool.
2. Rinse the rice under cold running water until the water runs clear. Add the rice and 810 milliliters water (see Cook’s Note) to a rice cooker and cook according to the manufacturer's instructions. When done, remove it from the cooker and spread it out in a pre-soaked wooden mixing tub (sushi oke) or on a sheet pan or tray. Immediately sprinkle it with the vinegar mixture and fold it in. Use a kitchen towel to very gently separate the rice grins and remove excess moisture and starch, being careful not to squeeze too hard or overwork the rice. Cool the rice before using, at least 15 to 20 minutes. Store the rice before use in a damp towel-lined sushi oke with a lid or in a covered bowl. Refrigerate any leftovers immediately.

Cured Mackerel:

1. Fillet the mackerel, leaving the rib bones in. Sprinkle the flesh side of each fillet with the salt. Cover with plastic wrap. Leave to cure at room temperature until the salt begins to pull moisture from the fish, 20 to 30 minutes or more, depending on the fat content of the fish (fatty mackerels will take a little longer than lean ones).
2. Rinse the salt off the fish after curing. Pat the fillets dry, then place them in a baking dish and cover with the vinegar. Place the kelp sheet over top. Refrigerate 25 to 40 minutes, depending on the fat content of the fish (fatty mackerels will take a little longer than lean ones).
3. Remove the fish fillets from the vinegar. Remove the rib and pin bones from the fillets. Carefully remove the skin by peeling it off with your fingers, making sure not to disturb the fatty, patterned layer underneath the skin. Pat dry with paper towels to remove any excess moisture. Makes 2 fillets.