Serves: makes 36
1 tablespoon corn oil
5oz/150g fresh tuna
6 sheets nori seaweed
rice wine vinegar for wetting
1 1/2lb/550g sushi nigiri
4oz/100g cooked spinach, thawed if frozen
2oz/50g pickled reg ginger, thinly shredded
Beat eggs in a bowl until foamy. Heat an omelette pan over medium heat with oil, add eggs and cook for about 1 minute until underside of omlette is light brown. Turn and cook for a further 30 seconds, then remove from the pan. Cut into strips and set aside.
Slice tuna into thin 1/4 x 3 inch (5mm x 7.5cm) strips. Divide all remaining ingredients into 4.
Lay 1 sheet nori on a bamboo rolling mat. Wet your hand with vinegar. Pat 1/4 rice evenly over nori, leaving a 1/2 inch (1cm) border. Arrange 1/2 spinach, tuna, egg and ginger in strips over rice. Roll up nori using bamboo mat, and press lightly but firmly to produce a neat cylinder. Repeat with remaining ingredients to make up 4 rolls.
Chill rolls for 1 hour, then slive each with a very sharp knife into 9 pieces.
Serve at room temperature.