Remove the silverskin and thick lumps of fat from the beef, if any. When cutting the meat, slice thinly and against the grain.
To a bowl, add sliced beef, ½ teaspoon salt, ¼ teaspoon white pepper, 1 teaspoon minced garlic, 1 teaspoon minced ginger, 2 teaspoon bicarb (baking soda), 1 teaspoon corn flour, and 2 teaspoon of dark soy sauce. Mix until well combined, then cover the bowl and set aside in the fridge for up to 1 hour. (overnight preferred).
Prepare the vegetables and cut them to stir-fry size. Thinly slice the mushrooms and cut the onion lengthwise, then set them aside.
To make the sauce combine 1 cup of beef stock with 1 tablespoon dark soy sauce, 1 tablespoon oyster sauce and a pinch of white pepper to taste, stir to combine, then set it aside.
Heat your wok to med-high until you begin to see it smoking, then add 2 tablespoon of vegetable oil. Add in the beef, making sure to spread it out evenly. Sear for 45 seconds, then rotate the beef to sear the opposite side for a further 45 seconds. Remove the beef, and then set it aside. Sear the beef in batches so as to not overcrowd the wok.
Over medium heat, add the onions and mushrooms to your wok and fry them until you begin to see the mushrooms lose their water. Add your vegetables, and turn the heat back to med-high. Stir the vegetables until slightly softened, then pour the sauce into your wok.
Using a spatula, deglaze the bottom of your wok until the sauce is brought to the boil. Then prepare 2 teaspoon of cornflour in 1 tablespoon cold water.
Add the cornflour to the sauce and stir immediately until the sauce has thickened. Finally, add 2 tablespoon of Lee Kum Kee Black Bean Garlic Sauce to the wok and stir until well combined.
Introduce the beef back into the wok with your wok-ready noodles, and stir to combine with the vegetables and the meat is cooked through.
Serve immediately and garnish with spring onion if you would like.