!! must be prepared at least 12 hours ahead !!
1 nice piece of tuna of regular shape (~200g)
sesame seed oil
prepared ponzu sauce
Prepare a bowl of icy water (water with a few ice cubes).
Prepare a large enough piece of kitchen film (saran wrap).
Sear the salmon piece on all sides in
a very hot pan with a little bit of high temperature oil (grape seed oil).
Sear on all faces for 15 s (20 s max) using tongs (be careful not to damage the tuna by squeezing too hard).
Place the tuna on the film and dip it in the ice water to cool quickly (to stop the cooking).
Prepare a marinade of:
1 part soja sauce
1+ part rice vinegar
2 part sake
0.2 to 0.3 part sesame seed oil
~2 cm grated ginger root.
Pour it in a ziploc bag, with the tuna and let marinate 12+ hours, turning it one of twice to spread the marinade evenly.
Cut in thin slices against the grain (3 to 4 mm).
Dip in ponzu sauce as for sushi.