Bring a large pot of salted water to the boil and blanch the spinach in batches, cooking only as much as will fit in the pot comfortably. Put a batch in, bring the water back to the boil and then take the spinach out and plunge it into a bowl of cold water, stirring gently. When all the spinach has been cooked and refreshed, tip it into a colander and drain. Take handfuls of it and squeeze as tightly as you can to remove excess moisture. Gently pull these handfuls apart to loosen the spinach.
Now lay your sushi rolling mat, with the bamboo running from left to right, on a clean cloth and put one-third of the spinach on to it. Form the spinach into a long sausage shape that runs along the middle and parallel to the bamboo. Take the end of the mat nearest you and fold it over the spinach, then roll the whole mat up tightly into a tube and roll it back and forwards to shape the spinach. Unroll the mat and do the same to the rest of the spinach.
Cut each roll of spinach into six sections with a very sharp knife and stand the sections on their ends. Place a small mound of pickled ginger on each, sprinkle with the mixed black and white sesame seeds and season with the tamari.
© 1997 Peter Gordon. All rights reserved.