Unagi Sauce Recipe

If unagi head & bone should be uncooked, broil over medium heat. Simmer sake/mirin over medium heat until sake-smell is gone. Add soy sauce and unagi head/bone, then simmer for 10 minutes. Be careful in heating sake/mirin, lest the liquid should catch fire. And it is adding broiled unagi head and bones that gives the "tare" authentic aroma and taste. Please find them. If you cannot, maybe adding a little bit of tariyaki sauce will be of some help.