Step 1

Scrub and rinse clams. Soak in a large bowl of cold water for 5 minutes. Drain thoroughly.

Step 2

Heat a wok or large saucepan over high heat. Quickly pour in the sake, mirin and rice vinegar. Add the clams; cover and cook until the clams open, 3 to 4 minutes. Discard any clams that do not open.

Step 3

Remove any scum that forms on the surface using a spoon or paper towel. Stir in the butter, soy sauce and green onion, tossing to coat the clams as the butter melts. Arrange clams on a serving plate and drizzle the sauce over them. Serve immediately.