Thinly slice the pork. Add salt (or skip the salt if you want a less salted dish), Shaoxing wine, oyster sauce, and white pepper. Mix well.
Add water or stock in. Grasp the pork slice for 2-3 minutes until all the juice is well absorbed, then add cornstarch. Set aside for 15minutes. Mix in around 1/2 tablespoon of vegetable cooking just before frying.
Heat your wok or pan first. Add cooking oil to form a 2-3 cm high layer (do not be scared by the oil amount, we do not eat them all). Spread the pork sliced in when the oil begins to warm but not hot. Let them stay for around 3-5 seconds and then quickly fry them until turns pale. Transfer out immediately.
Remove the extra oil and save them for vegetable stir fries. Keep around 1 tablespoon of oil and fry garlic, ginger and scallion until aromatic. Place shiitake mushroom in, add oyster sauce and light soy sauce. Fry for around 30 seconds until the shiitake mushrooms are just cooked.
Return pork and add scallion sections, drizzle sesame oil. Quickly mix well and transfer out. Serve hot!
Notes
You can use either pork tenderloin or pork butt for this recipe. For a better texture, I recommend pork butt which is the best part for stir-frying in my mind. If you prefer a better shape of the dish, pork tenderloin is a better choice.