Step 1: Prepare the Angus steak. Pat the steak dry with paper towels. Slice the steak against the grain into 1/2-inch thick pieces.
Step 2: Marinate the beef. In a medium bowl, whisk together the marinade ingredients: 1 tbsp Shaoxing wine, 1 tbsp light soy sauce, 1 tsp cornstarch, and 1/2 tsp white pepper. Add the sliced beef and toss to coat evenly. Let it marinate at room temperature for at least 30 minutes, or refrigerate for up to 4 hours.
Step 3: Prepare the sauce. In a small bowl, combine the sauce ingredients: 2 tbsp Shaoxing wine, 1 tbsp dark soy sauce, 2 tbsp light soy sauce, 1 tbsp oyster sauce, 1 tbsp sugar, 1/2 tsp white pepper, and 1 tbsp cornstarch. Whisk until well combined and smooth, ensuring no lumps from the cornstarch.
Step 4: Sear the beef. Heat a large skillet or wok over medium-high heat. Add 1 tbsp vegetable oil. Once the oil shimmers, add the marinated beef in a single layer, making sure not to overcrowd the pan. Sear for 1-2 minutes per side until beautifully browned. Remove the seared beef from the pan and set aside. Cook in batches if necessary.
Step 5: Sauté aromatics. In the same pan, add another splash of oil if needed. Add the minced garlic and sliced ginger. Sauté for about 30 seconds until fragrant, being careful not to burn the garlic.
Step 6: Finish the dish. Pour the prepared sauce mixture into the pan with the aromatics. Bring to a simmer, stirring constantly, until the sauce thickens and becomes glossy, about 1-2 minutes. Return the seared beef to the pan, tossing gently to coat all the pieces evenly with the sauce. Cook for another 1-2 minutes, allowing the beef to finish cooking and absorb the sauce.
Step 7: Serve. Garnish the shanghai angus steak with chopped green onions and sesame seeds. Serve immediately with steamed rice or your preferred side.