Pat the shrimp dry with a paper towel and place them in a bowl. Marinate with salt, white pepper, light soy sauce, baking soda, shaoxing wine, cornstarch and oil. Let marinate for 15 minutes while you prepare the rest of your ingredients.
I always make sure the shrimp are fairly dry before they hit the marinade, because surface moisture can dilute the coating. After 15 minutes, they should look lightly glossy and a little velvety rather than wet and drippy.
In a small bowl, make the sauce by adding soy sauce, oyster sauce, dark soy sauce, shaoxing wine, sesame oil, white pepper, sugar, water, cornstarch and msg. Mix until the cornstarch and sugar is dissolved.
Give this a really good stir so you do not end up with cornstarch hiding at the bottom. The sauce should look smooth and thin at this stage, almost too thin, but it thickens fast once it hits the hot pan.
Bring a large pot of water to a boil over high heat. Cook the lo mein noodles 2 minutes less than package directions, drain, then rinse with cold water and drain dry. Coat the noodles with sesame oil to prevent sticking.
This undercooking step matters. You want the noodles to still have a noticeable bite in the center, because they finish in the wok. After rinsing, drain them well so you are stir-frying noodles, not steaming them.
In a large wok or pan, heat 3 tbsp of oil over high heat until just smoking. Sear the shrimp for 2-3 minutes or until cooked through and set aside.
You should hear an immediate sizzle. The shrimp are ready when they turn opaque and curl into a loose C shape. If they tighten into little O’s, they have gone a bit too far. For food safety, shrimp are done at 145°F and opaque throughout.
In the same oil, sauté the garlic and ginger for 15 seconds over medium high heat. Add the scallion whites, carrot, cabbage, white onion, and mushrooms. Turn the heat to high and sauté for a 2-3 minutes until slightly wilted, then add the noodles, shrimp, and sauce and mix thoroughly. Continue cooking for 1-2 minutes until the sauce has thickened and is evenly coated. Add scallion greens and bean sprouts, mix and stir fry for another minute and enjoy!
The garlic and ginger should smell sharp and fragrant almost immediately, so do not wander off here. Once the noodles and sauce go in, keep everything moving until the noodles turn glossy and evenly bronzed. I personally love separating the scallion whites and greens because the whites build flavor early, while the greens stay fresh and bright at the end.