Step 1: Marinate the Beef

1. In a bowl, mix the sliced flank steak with soy sauce, cornstarch, and vegetable oil. Let it marinate for at least 15 minutes.

Step 2: Prepare the Stir-Fry

1. In a large skillet or wok, heat 1 tablespoon of vegetable oil over medium-high heat.
2. Add the broccoli florets and stir-fry for about 2–3 minutes until bright green and slightly tender. Remove from the pan and set aside.

Step 3: Cook the Beef

1. In the same skillet, add the remaining 1 tablespoon of vegetable oil.
2. Add the marinated beef to the skillet in a single layer and cook for 2–3 minutes until browned and cooked through. Remove the beef and set aside.

Step 4: Combine Ingredients

1. In the same skillet, add the white parts of the scallions, minced garlic, and ginger. Sauté for about 30 seconds until fragrant.
2. Return the broccoli and beef to the skillet. Pour in the beef broth, soy sauce, oyster sauce (if using), and sesame oil. Stir to combine and cook for an additional 1–2 minutes until heated through.

Step 5: Serve

1. Season with salt and pepper to taste. Garnish with the green parts of the scallions before serving.
2. Serve hot over steamed rice or noodles.