Thaw rice cake rolls in refrigerator overnight.Let stand at room temperature for 2 hours before cooking.Partially freeze beef.Bias-slice beef across the grain into thin bite-size strips.Place beef in a plastic bag set in a deep bowl.Combine soy sauce,sherry,2 green onions and gingerroot.Pour over beef.Close bag.Marinate in the refrigerator for 1 to 2 hours,turning bag occasionally to distribute marinade.Drain well,reserving marinade. Bias-slice rice cake rolls into 1/4" slices.Heat 2 tbsp. of the oil in wok.Add bok choy,mushrooms,bamboo shoots,2 green onions and chives. Stir-fry 3 minutes or until bok choy is crisp-tender.Remove vegetables and juices from wok.Heat remaining oil in wok.Add beef.Stir-fry 3 minutes or until no longer pink.Remove from wok. Add 1/4 cup chicken broth and reserved marinade to wok.Add sliced rice cake rolls.Stir constantly for 2 to 3 minutes or until rice cake slices soften,add more chicken broth as necessary to prevent rice cake slices from sticking together.Return beef and vegetables to wok.Heat through.Serve immediately.Makes 4 servings.