Step 1: Prepare the Beef. In a medium bowl, combine the thinly sliced beef with 1 tablespoon soy sauce, 1 tablespoon cornstarch, and 1 teaspoon sesame oil. Mix well to coat the beef evenly. Let it marinate at room temperature for at least 30 minutes, or refrigerate for up to 2 hours. This tenderizes the beef and helps it brown beautifully.
Step 2: Whisk the Sauce. In a small bowl, combine the beef broth, 1/4 cup soy sauce, oyster sauce (if using), rice vinegar, brown sugar, grated ginger, minced garlic, 1 teaspoon cornstarch, and 1/2 teaspoon sesame oil. Whisk until the brown sugar is dissolved and the cornstarch is fully incorporated. Set aside.
Step 3: Prepare the Broccoli. Bring a pot of lightly salted water to a boil. Add the broccoli florets and blanch for 1-2 minutes until vibrant green and crisp-tender. Drain immediately and plunge into an ice bath to stop the cooking, then drain thoroughly. Alternatively, you can steam the broccoli.
Step 4: Cook the Beef. Heat 1 tablespoon of vegetable oil in a large skillet or wok over medium-high heat until shimmering. Add half of the marinated beef in a single layer, ensuring not to overcrowd the pan. Sear for 1-2 minutes per side until browned. Remove the cooked beef from the pan and set aside. Repeat with the remaining beef and the second tablespoon of oil.
Step 5: Combine and Finish. Return all the cooked beef to the skillet. Give the prepared sauce a quick whisk again (cornstarch settles!) and pour it over the beef. Bring the sauce to a gentle simmer, stirring constantly. The sauce will begin to thicken as it cooks, typically within 1-2 minutes.
Step 6: Add Broccoli and Serve. Stir in the blanched broccoli florets and toss to coat everything in the glossy sauce. Cook for another minute or two until the broccoli is heated through. Remove from heat. Serve immediately over steamed rice or noodles, garnished with sesame seeds if desired. Enjoy your delicious homemade Beef and Broccoli Recipe!