1Marinate beef for 15 minutes. Mix sauce ingredients in a bowl. Separate fresh noodles.
2Heat pan over high heat. Sear beef in batches for 2–3 minutes until browned and slightly charred, letting it sit undisturbed for 1 minute before flipping. Remove from pan.
3Reduce heat to medium high, then add oil, onion, garlic, and ginger. Stir-fry for 1–2 minutes until fragrant.
4Add Chinese broccoli stems and cook for 2 minutes, then add leaves and cook a further 1–2 minutes until wilted. Remove from pan.
5Increase pan heat, add noodles to the hot pan and let sit undisturbed for 30 seconds to lightly char. Toss gently, then add sauce and cook for 1 minute until evenly coated.
6Return beef and vegetables to the pan and toss for 1–2 minutes until glossy and combined. Add bean sprouts and spring onions in the final 30 seconds. Serve immediately.