The Japanese sear-and-slice technique — spectacular with premium Port Lincoln bluefin and almost embarrassingly quick.
Whisk soy, mirin, rice vinegar, sesame oil, and grated ginger. Set aside.
Pat tuna dry. Roll firmly in sesame seeds, pressing to adhere.
Heat a dry pan over very high heat until smoking.
Sear tuna 20 seconds on each of the 4 sides. The centre must stay raw.
Immediately transfer to a plate and rest 2 minutes.
Slice against the grain into 1cm slices. Fan on a plate. Spoon over the dressing. Top with spring onion.
Chilled sake (Junmai Daiginjo) or a dry Clare Riesling.