Place mackerel fillets in a dish,
cover completely with plenty of salt and leave overnight in the
refrigerator.
Make vinegar rice.
Remove mackerel and rub off salt
with absorbent kitchen paper.
Carefully remove all bones with
tweezers.
Wash off any remaining salt with
rice vinegar.
Using your fingers, remove
transparent skin from each fillet, leaving silver pattern on flesh
intact.
Place a fillet, skinned side down,
in a wet wooden mould or rectangular container, about 25 x 7.5 x 5
cm (10 x 3 x 2 in), lined with a large piece of cling film.
Fill gaps with small pieces taken
from the other fillet so the mould is lined.
Press vinegar rice down firmly
on top of fish with fingers.
Put the wet wooden lid on, or fold
in cling film, and place on weight on top.
Leave in cool place (but do not
refrigerate) for several hours.
Remove from container, unwrap, and
cut into small pieces with a sharp knife, wiping the knife with a
vinegar soaked cloth or paper after each cut.
Garnish with lemon, cress, and
vinegar ginger slices, if wished.
Serve with soy sauce handed
separately in small individual dishes.