Place spinach in a dry pot over medium-high heat and stir continually until spinach just begins to wilt
transfer into a colander to cool
While spinach is cooling, use a mortar and pestle to grind sesame seeds into a coarse paste. Then add sugar, soy, and mirin and mix to combine
Squeeze cooled spinach to remove liquid and chop roughly.
Stir spinach and dressing together, then cover and chill until ready to serve