01 - Combine sliced beef with soy sauce, cornstarch, sesame oil, and black pepper in a bowl. Toss thoroughly to coat and let marinate for 10–15 minutes at room temperature.
02 - Whisk together soy sauce, oyster sauce, cornstarch, brown sugar, and beef broth in a small bowl until cornstarch dissolves completely. Set aside for later use.
03 - Heat 1 tablespoon vegetable oil in a large skillet or wok over high heat until smoking. Add marinated beef in a single layer and stir-fry for 2–3 minutes until just browned. Remove beef from pan and set aside on a plate.
04 - Add remaining 1 tablespoon oil to the pan. Add broccoli florets and stir-fry for 2 minutes. Add 2 tablespoons water, cover tightly, and steam for 2–3 minutes until broccoli is bright green and tender-crisp.
05 - Uncover the pan and add minced garlic and ginger. Stir-fry constantly for 30 seconds until fragrant, being careful not to burn the garlic.
06 - Return beef to the pan along with any accumulated juices. Pour in the prepared sauce and toss everything together. Cook for 1–2 minutes, stirring constantly, until sauce thickens and coats the beef and broccoli evenly.
07 - Transfer to a serving platter or individual plates. Serve immediately over steamed rice or noodles if desired.