Cook the ramen noodles following the directions onthe package, then drain. Ringse the noodles to remove the starch, then drain in a fine-mesh colander and set aside.
Cut the beef into thin strips and leave to thaw completely while preparing the remaining ingredients.
Heat the chicken stock in a saucepan, add the ginger and garlic, and simmer gently over medium heat 10 minutes. Remove the flavorings using a slotted spoon and discard. Season the broth with the sake, shoyu and salt and pepper to taste, then remove from the heat.
Stir-fry the bok choy in 1 T. of the oil in a skillet or wok over medium heat 1 to 2 minutes, then transfer to a plate. Add the remaining oil to the pan and stir-fry the shiitake and beef over medium heat 2 to 3 minutes until the meat turns pale. Season with 1 T. of the shoyu and salt and pepper and remove fromthe heat.
Pour boiling water over the cooked noodles to warm them, then drain them and divide between 4 bowls. Spoon the soup over the noodles and top with the beef, shiitake, and bok choy. Serve hot.