Combine the sherry, ginger, soy sauce, 1 tbsp oil, brown sugar, corn starch, garlic, red pepper flakes, and beef in a resealable plastic bag and seal. Turn several times to coat and marinate 30 minutes at room temperature, or refrigerate for up to 24 hours.
Heat a large wok or pot over high heat. Add 1 tsp oil. Lift the beef from the marinade with a slotted spoon, reserving the marinade. Quickly stir-fry the beef until lightly browned on both sides, about 1-2 minutes. Remove from the pan and set aside.
Add the remaining oil and stir-fry the bok choy, shitakes, scallions, and carrots for 1-2 minutes. Add the reserved marinade, stock, water, and hoison sauce. Bring to a boil. Stir in the noodles and simmer until tender, about 8-10 minutes. Return the beef to the wok or pot, cooking just long enough for the beef to heat through. Finish with a few drops of Chinese hot pepper oil. Do not let it sit before serving, or the noodles with absorb the liquid and swell!