In a small bowl, whisk together beef broth and cornstarch. Add sliced beef and toss until coated. Set aside to marinate for 10 minutes.
Make the Sauce:
In another bowl, combine soy sauce, oyster sauce, brown sugar, garlic, ginger, and sesame oil. Stir until smooth.
Cook the Beef:
Heat cooking oil in a large skillet or wok over medium-high heat.
Add beef in a single layer and sear for 2–3 minutes until browned (do not overcook). Remove and set aside.
Cook the Broccoli:
In the same skillet, add broccoli florets with a splash of water. Stir-fry for 3–4 minutes until tender-crisp.
Combine Everything:
Return beef to the pan, pour in the sauce, and stir until everything is evenly coated and heated through.
Cook for another 1–2 minutes until the sauce thickens slightly.
Serving and Storage Tips
