Tender beef and flat rice noodles are wok-fried with soy sauce and bean sprouts for a quick, smoky meal. High in protein and ready in minutes, this family dinner staple embodies fast, flavorful Chinese cooking.
Slice the beef flank steak thinly against the grain and marinate with 1 tbsp light soy sauce and 0.5 tsp white pepper. Set aside for at least 10 minutes.
Loosen fresh flat rice noodles gently; if refrigerated, briefly microwave to soften. Slice green onions into 2-inch lengths, and thinly slice yellow onion.
Heat 1.5 tbsp vegetable oil in a wok over high heat until shimmering. Add the beef and stir-fry rapidly for about 1 minute until just browned. Remove beef to a plate.
Add remaining 1.5 tbsp oil to the wok. Stir-fry onion and most of the green onions for 30 seconds over high heat, then add rice noodles. Drizzle with light and dark soy sauce, oyster sauce, sugar, and toss quickly to combine and evenly coat the noodles.
Return the beef to the wok, add bean sprouts, and stir-fry everything together over high heat for 1-2 minutes until heated through, noodles are slightly charred, and bean sprouts still crisp. Finish with a drizzle of sesame oil and serve hot.