1 (5 ounce)* piece of a sushi-grade salmon belly, skin on
1 (5 ounce)* piece of sushi-grade tuna loin
1 (5 ounce) piece of sushi-grade tuna belly
To prepare the salmon:
Wrap the salmon in plastic and freeze for 48 hours. Transfer to the refrigerator and defrost slowly overnight. (This will kill any parasites without damaging the fish.) Before you are ready to prepare the sashimi, pull the frozen salmon out of the freezer and let it defrost slowly in the refrigerator over the period of a day. Make sure to dry salmon very well once defrosted.
Lay the fish skin side down on a cutting board. Holding a long, sharp slicing knife parallel to the cutting board, remove the skin from the fish by using long strokes to slice just between the skin and the flesh from one end of the piece to the other. The final piece of fish should be 3-fingers wide. If the piece of fish is very narrow, slice it on a greater bias to achieve a 3-finger wide slice.
Using the same long strokes, cut ¼ inch slices across the grain. Serve immediately.
To prepare the tuna loin for sashimi & nigiri:
If you did not have your fishmonger cut your piece of fish, you will have to cut it into smaller shapes before slicing the fish. Cut the loin into “4-finger” width by “2-finger” width pieces for nigiri, or “3-finger” width by “2-finger” width pieces for sashimi, which should yield a 1 1/2″ x 3” x 4” size piece.
Once you have those pieces, slice each one across the grain into ¼ inch slices, using long strokes.
To prepare the tuna belly for the spicy tuna roll:
For any piece of tuna that is heavy in sinew, remove the sinew using a spoon. Holding the spoon downwards towards the cutting board, scrape the flesh of the tuna from the sinew, using the other hand to hold the sinew down. Once all of the tuna has been scraped from the sinew, discard the sinew.
Collect the scraped tuna in a bowl and mix with spicy mayo for a spicy tuna roll. (See spicy tuna roll recipe.)