Slice the pork loin into thick pieces, then cut into strips. Marinate with salt, white pepper, cornstarch, and oil. Set aside.
Boil the thick wheat noodles for 2–3 minutes, until almost cooked through but still slightly firm in the center.
Rinse the noodles under cold water and drain well.
Mix the noodles with light soy sauce, dark soy sauce, and oil. Set aside. (see note 1)
Heat a wok or large pan over medium-high heat. Add oil. Stir-fry the meat until it just changes colour.
Add the shiitake mushrooms and cook until lightly browned and fragrant.
Add the noodles, light soy sauce, dark soy sauce, sugar, and lard if using.
Toss until the noodles are evenly coated and glossy.
Add the baby bok choy and stir-fry until just wilted.
Taste and add salt if needed. Serve hot.