Combine sliced flank steak with baking soda, cornstarch, and soy sauce in a bowl. Mix well and let marinate for 10 minutes.
Gently separate the fresh rice noodles and set aside. Cut scallions into 2-inch pieces and slice ginger.
Heat 1 tablespoon oil in a large wok or skillet over high heat. Add marinated beef and stir-fry until just cooked through and pale in color, about 2-3 minutes. Remove and set aside.
Add remaining oil to the wok. Add ginger slices and stir-fry for 30 seconds until fragrant.
Add rice noodles to the wok and gently stir-fry for 1-2 minutes, breaking them apart carefully.
Add scallions and bean sprouts, stir-frying for another minute.
Return beef to the wok and add Shaoxing wine, dark soy sauce, and sugar. Toss everything together for 1-2 minutes.
Season with salt and white pepper to taste. Serve immediately while hot.