Tuna dish is called Maguro Butsu. When preparing big fish like tuna or swordfish for sashimi, Japanese fishmongers cut them lengthways to make a long rectangular shape. After the prime parts are cut out, the trimmings are sold cheaply. Butsu is a chopped trimming, and it has all the quality of the best tuna sashimi.
400g/14oz very fresh tuna, skinned
1 carton mustard and cress (optional)
20ml/4teaspoons wasabi paste from a tube, or the same amount of wasabi power mixed with 10ml/2teaspoon water
8 spring onions (scallions), green part only, finely chopped
4 shiso leaves, cut into thin slivers lengthways
1.Cut the tuna into 2cm/3/4in cubes. If using mustard and cress, tie into pretty bunches or arrange as a bed in four small serving bowls or plates.
2.Just 5-10 minutes before serving, blend the wasabi paste with the shoyu in a bowl, then add the tuna and spring onions. Mix well and leave to marinate for 5 minutes. Divide among the bowls and add a few slivers of shiso leaves on top. Serve immediately.