Volcano Roll

Rinse 360g short-grain sushi rice under cold running water for 3 minutes until the runoff water is nearly clear. Combine rinsed rice with 480ml (2 cups) cold water in a rice cooker, run the standard white rice cycle, then let the rice steam, covered, for 15 minutes after the cycle completes. While the rice is still warm, gently fold in a heated mixture of 60ml rice vinegar, 25g granulated sugar, and 5g fine sea salt (microwaved for 30 seconds to fully dissolve solids). Spread the seasoned rice across a wooden tray to cool to room temperature (21C/70F); do not refrigerate, as this will make the rice hard and grainy.

Shred 170g crab meat into loose, even strands, then pat completely dry with paper towels to remove excess moisture. Cut the seeded 150g English cucumber into 6mm (1/4-inch) thick strips that match the length of a nori sheet. Slice 150g ripe avocado into matching 6mm strips, toss gently with 5ml fresh lemon juice to prevent browning, and take care not to mash the soft flesh. Arrange all prepped fillings within arm’s reach of a bamboo rolling mat tightly wrapped in plastic wrap.

Lay one full nori sheet shiny-side down on the prepared bamboo mat. Dip your hands in vinegared water (remaining 15ml rice vinegar mixed with 240ml/1 cup cold water) to prevent sticking, then spread 1/4 of the cooled seasoned rice (approx 150g) in an even 5mm (1/5-inch) thick layer across the nori, leaving a 2cm (3/4-inch) bare strip at the top edge to seal the roll. Sprinkle 1/4 of the toasted sesame seeds over the rice, then flip the nori so the rice side faces down against the mat. Arrange 1/4 of the crab, cucumber, and avocado in a straight, tight line across the center of the nori. Roll the mat firmly from the bottom edge upward, squeezing gently to form a tight, uniform log, sealing with the bare nori edge moistened with a dab of water. Repeat to make 4 total rolls, placing them seam-side down on a parchment-lined baking sheet.

In a medium glass mixing bowl, combine 225g finely diced raw shrimp, 80ml Kewpie mayonnaise, 45ml Sriracha, and 30g masago, stirring until every piece of shrimp is evenly coated in the creamy, bright orange-pink sauce. Taste and adjust spice level if desired, adding 5ml (1 tsp) extra Sriracha for more heat. Spoon 1/4 of the topping mixture in a thick, mounded line directly down the center of each rolled sushi log, spreading it slightly to cover the top 2/3 of each roll to mimic the sloped shape of a volcano. Sprinkle 7.5g (1 tbsp) of shredded mozzarella evenly over the topping on each roll.

Preheat oven to 220C/425F. Place the baking sheet with topped rolls on the middle oven rack, and bake for 8-10 minutes, until the shrimp is fully opaque and cooked through, the topping is bubbling around the edges, and the corners of the nori are slightly crisp. Do not overbake, as this will make the rice tough and the avocado bitter. Remove the baking sheet from the oven and let the rolls rest for 2 minutes at room temperature before slicing.

Dip a sharp, thin-bladed knife in cold vinegared water between cuts to prevent sticking, then slice each roll into 6 even 2.5cm (1-inch) thick pieces. Arrange slices on a serving platter with the baked topping facing upward to show the dramatic 'lava' effect, drizzle with extra Sriracha-mayo mix if desired, and serve alongside 60ml low-sodium soy sauce for dipping.