Marinate the Beef:
In a medium bowl, combine soy sauce, cornstarch, oyster sauce, and sesame oil. Add the sliced beef and toss to coat evenly. Let it marinate for 10–15 minutes while you prepare the rest of the ingredients.
Tip: Slicing the beef thinly against the grain keeps it tender and prevents chewiness.
Make the Sauce:
In a small bowl, whisk together soy sauce, beef broth, brown sugar, oyster sauce, cornstarch, rice vinegar, garlic, and ginger until smooth. Set aside.
Tip: The cornstarch will help the sauce thicken into that classic glossy texture.
Cook the Broccoli:
Heat 1 tablespoon of oil in a large skillet or wok over medium-high heat. Add the broccoli and ¼ cup water, cover, and steam for 2–3 minutes until bright green and slightly tender. Remove from the pan and set aside.
Sear the Beef:
Add the remaining tablespoon of oil to the skillet. When hot, add the beef in a single layer (cook in batches if needed). Sear for 1–2 minutes per side until browned and just cooked through. Remove from heat.
Combine Everything:
Pour the sauce into the same skillet and cook for 1–2 minutes until it thickens and bubbles. Return the beef and broccoli to the pan, toss everything together, and cook for another 1–2 minutes until evenly coated.
Serve:
Sprinkle with sesame seeds and green onions if desired. Serve hot over rice or noodles.