Marinate the Beef – Toss the sliced beef with 1 tablespoon of cornstarch and a little soy sauce. Let it sit for 10 minutes to tenderize.
Cook the Beef – Heat 1 tablespoon of vegetable oil in a pan or wok over high heat. Stir-fry the beef for 2-3 minutes until browned. Remove and set aside.
Sauté the Aromatics – In the same pan, add another tablespoon of oil. Stir-fry the sliced onions for 2 minutes until slightly softened. Add garlic and ginger, cooking until fragrant.
Prepare the Sauce – Stir in soy sauce, oyster sauce, sugar, beef broth, sesame oil, black pepper, and rice vinegar. Let it simmer for a minute.
Combine & Thicken – Return the beef to the pan and mix well. Stir in the cornstarch slurry and cook until the sauce thickens.
Garnish & Serve – Top with chopped green onions and sesame seeds. Serve hot over steamed rice or noodles.