Fill a 4- to 5-quart pot three-quarters full of water and bring to a rolling boil.

Drop the spinach into it. Push the spinach down, if necessary. Cook the spinach 2 to 3 minutes or until it has wilted completely.

Drain spinach in a colander. Run some cold water over the spinach to cool it off and fix its bright-green color. Squeeze all the water out of the spinach and put it into a bowl.

Add the soy sauce, mirin, and crushed sesame seeds.

Mix well. Divide into four portions.

Make hillocklike piles of each portion. Place the hillocks in the center of four small Japanese or Chinese dishes. Serve at room temperature.