01 - Combine sliced beef with 2 tbsp soy sauce, 1 tbsp 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.
03 - Heat 1 tbsp 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 browned on edges. Remove beef from pan and set aside.
04 - Add remaining 1 tbsp oil to the pan. Add broccoli florets and stir-fry for 2 minutes. Add 2 tbsp water, cover tightly, and steam for 2–3 minutes until broccoli turns bright green and reaches tender-crisp texture.
05 - Uncover pan and add garlic and ginger. Stir-fry for 30 seconds until fragrant, being careful not to burn the garlic.
06 - Return beef to the pan. Pour in prepared sauce and stir constantly for 1–2 minutes until sauce thickens and glossy coats the beef and broccoli evenly. Serve immediately.