For the sauce: Mix together the stock, 3/4 cup water, the cornstarch and soy sauce. Stir well and set aside. For the noodles: Bring a pot of water to a boil, and then add the noodles and cook until al dente, 3 minutes. Drain under cold running water. Add the sesame oil to prevent the noodles from sticking together.
Heat a wok over high heat and add the peanut oil. Add the ginger, mushrooms and garlic and toss together for a few seconds. Then add the shrimp and cook, stirring, for less than 1 minute. Add the choi sum leaves and toss together for 1 minute. As the shrimp starts to turn pink, add the Shaosing rice wine.
Pour in the sauce and bring to a boil; this will take 1 to 2 minutes. Quickly add the cooked egg noodles and season with the sesame oil and dark soy. Stir together well for 1 minute, making sure all the noodles are coated in the sauce. Season the ground white pepper and transfer to a serving bowl. Serve immediately.
If using dried shitake mushrooms, you can use the steeping water to soften the mushrooms instead of vegetable stock.