Make shiraga negi (onion garnish). Cut the root end off the green onion, cut off the green tops, and then cut the remaining white section into inch-long pieces. To each white section, make a lengthwise cut without cutting all the way through, and remove the core. Lay the outer layers flat and then cut them lengthwise into very thin strips. Soak the cut pieces in ice water for 30 minutes. Drain and pat dry.