De-sand the manila clams and rub the shells together to rinse. *Get rid of any slime on the surface.
Put the manila clams and the sake into a pot, and cover with a lid. Steam the clams with sake over high heat as you shake the pot gently. When the clams open up, add the water.
Simmer the clams over medium heat, and skim off any scum on the surface. Turn the heat off and whisk in the miso. Dish it up into a bowl, and scatter some green onion rounds.
Story Behind this Recipe
I got tons of clam when I went clam-digging, and had them steamed in sake. Then I made miso soup with the leftovers, which turned out to be really tasty. Since then, I've been making manila clam miso soup this way.
Use less miso than you regularly use to make miso soup. This particular miso soup will be tasty enough from the savory and rich flavor from the manila clams steamed in sake. Don't simmer too much after the clams open up (for a more plump result). I also make clear soup with manila clams steamed in sake. I highly recommend that, too.