Negitoro Onigiri (Minced Tuna Rice Ball)

Shiojime (optional step for improved texture & flavor). Wash and dry 60 g sashimi grade tuna block, then sprinkle with salt all over and place it in a container. Store the container in the fridge for 10-15 minutes with one side elevated to drain the excess moisture. Wash off the salt and pat dry with kitchen paper.
Use a spoon to scrape the tuna flesh.
Chop with a knife until it becomes roughly mashed.
Place the mashed tuna in a bowl and add ½ tbsp Japanese mayonnaise, ½ tsp cooking oil and ⅛ tsp dashi granules. Mix until combined.
Measure out 440 g cooked Japanese short-grain rice and divide it into equal portions. If using a rice ball mold, sprinkle a pinch of salt into the mold and add half a portion (approx 55g / 2oz) of rice. Make a dent in the center and add a spoonful of mashed tuna.
If shaping by hand, wet your hands and sprinkle them with a pinch of salt. Take a portion of rice (approx 110g / 4oz) and spread it flat on your palm, placing the tuna in the center. (Wet hands to prevent sticking.)
Top the tuna with a small blob of wasabi and a few finely chopped green onions. Add 1 drop of Japanese soy sauce (koikuchi shoyu).
For the mold, cover with the other half of the rice and sprinkle with a pinch of salt. For hand-shaping, fold the rice over and then shape into a rounded triangle.
Wrap with nori and enjoy!