Slice the beef: Freeze the steak for 15 minutes for cleaner cuts. Slice thinly against the grain.
Marinate: Toss beef with light soy, cornstarch, Shaoxing wine, sesame oil, and sugar. Set aside 10–15 minutes.
Mix the sauce: Combine all sauce ingredients in a small bowl. Keep it nearby.
Prep noodles: If using fresh refrigerated ho fun, gently separate by hand. If stiff, microwave 15–20 seconds to loosen. If using dried rice noodles, soak per package until pliable, then drain and pat dry.
Dry your veg: Pat bean sprouts and scallions dry so they sear, not steam.
Use a carbon steel wok if you have it. A large cast-iron or stainless skillet works too.
Heat the pan until it lightly smokes. Add 1–2 tablespoons oil and swirl to coat.
Lay the beef in a single layer. Let it sear undisturbed for 30–45 seconds to brown.
Stir-fry another 30–60 seconds until mostly cooked but still a hint pink. Transfer to a plate.
Add a teaspoon more oil. Toss in onion and stir-fry 1 minute until edges char.
Add garlic. Stir 10–15 seconds until fragrant.
Add bean sprouts and half the scallions. Toss 30–45 seconds to keep them crisp.
Add the rice noodles. Drizzle 1 teaspoon oil around the edges to prevent sticking.
Pour in the sauce. Toss gently with a spatula and chopsticks to coat without shredding the noodles.
Return the beef and any juices. Add remaining scallions. Stir-fry 30–60 seconds until glossy and hot.
Taste and adjust salt with a splash of light soy or a pinch of sugar if needed.
Plate immediately. Top with chili oil and sesame seeds if you like heat and crunch.
Serve with extra bean sprouts or a simple cucumber salad for contrast.
