Leave Kombu in water for 30 minutes in a pot. Cut Mitsuba leaves into pieces, 1" (2.5cm) long. Set aside.
Add Hamaguri in the Kombu water, and start cooking at medium heat. Add Sake.
Just before boiling, remove Kombu and discard. Remove any scum on the surface of the soup, and continue cooking until shells open up. Season with salt and Soy Sauce.
Pour into bowls, and top with Mitsuba leaves.