Add spinach to 6 cups of rapidly boiling water in medium saucepan 2 1/2 or 3 minutes at most. Immediately pour into colander, gently rinse with cold water; drain. Take about half the cooled spinach at a time and gently squeeze out most of the water by hand, forming two hotdog-shaped rolls. Place on cutting board. Rolls should not be drippy.
Toast sesame seeds in small dry skillet over medium heat until slightly brown. Release their fragrance by pressing seeds with mortar and pestle. Or for the same effect, pour seeds into small bowl or cup and press with rounded back of and ice cream scoop or spoon.
Slice spinach rolls into 6 pieces each and place on serving dish, topping each piece with sesame seeds. As each person takes their serving, they put on a few drops of soy sauce to their liking.