Step 1: Prepare the Beef Marinade

• Slice the beef thinly against the grain to ensure tender results. Place the sliced beef into a bowl.
• Add the soy sauce, cornstarch, sugar, sesame oil, and ground white pepper. Mix well to coat the beef evenly. Let the beef marinate for at least 10 minutes while you prepare the other ingredients.

Step 2: Prepare the Sauce

• In a small bowl, whisk together the oyster sauce, soy sauce, sugar, and water. If you prefer a thicker sauce, add 1 teaspoon of cornstarch and stir until smooth. Set aside.

Step 3: Heat the Pan and Cook the Beef

• Heat 1 tablespoon of vegetable oil in a large wok or skillet over medium-high heat.
• Add the marinated beef in a single layer and sear for 1–2 minutes without stirring to allow it to brown. Flip and stir-fry for another 1–2 minutes until the beef is browned and nearly cooked through. Remove the beef from the pan and set it aside.

Step 4: Stir Fry the Onions

• Add the remaining tablespoon of vegetable oil to the same pan.
• Add the sliced onions and stir-fry for 3–4 minutes until they begin to soften and caramelize. Add the garlic and grated ginger and stir for an additional 30 seconds until fragrant.

Step 5: Combine the Beef and Sauce

• Return the beef to the pan and pour the prepared sauce over the beef and onions. Stir everything together to coat evenly. Let it cook for 1–2 minutes until the sauce thickens and the beef is heated through.

Step 6: Garnish and Serve

• Remove the pan from heat and garnish the stir fry with sliced green onions.
• Serve the Beef and Onion Stir Fry hot over steamed rice, noodles, or alongside stir-fried greens for a complete meal.