Note Most buckwheat is sold roasted. For this recipe, look for raw buckwheat, available from most health-food shops. Lamb eye fillet, also known as lamb tenderloin, is the smaller fillet from a lamb loin chop. (It's not to be confused with the backstrap, also known as the eye of loin, which is the larger fillet from the same chop.) Salted kombu, also known as shio kombu, is kelp that is thinly sliced, cooked in soy sauce and coated in a salt mixture. It's available from select Japanese grocers, including Tokyo Mart.