For the beef: Combine the flank steak, baking soda, cornstarch, soy sauce, and neutral oil.
Sauce: Combine the shaoxing, sesame oil, soy sauce, dark soy sauce, white pepper, and sugar.
Rest of dish: Heat 3 Tbs neutral oil in a wok or large skillet over high heat. Add the scallion whites, ginger, and garlic and stir-fry for 30 seconds. Add the beef and stir-fry for 1-2 minutes until no longer pink. Add the rice noodles and sauce and toss everything together for 2-3 minutes until the noodles are heated through. Garnish with the scallion greens.
