In a bowl, toss the beef slices with 1 tbsp soy sauce and 1 tbsp cornstarch. Let rest for 10 minutes.
Make the Sauce
In a small bowl, whisk together the remaining soy sauce, oyster sauce, hoisin sauce, vinegar, brown sugar, garlic, ginger, beef broth, and chili flakes (if using).
Cook the Beef
Heat 2 tbsp oil in a large skillet or wok over high heat.
Add the beef in a single layer and sear for 1–2 minutes per side until browned but still tender. Remove and set aside.
Finish the Sauce
In the same pan, add 1 tbsp oil. Pour in the sauce mixture and bring to a simmer.
Stir in 1 tbsp cornstarch mixed with 2 tbsp water if you prefer a thicker sauce.
Combine and Serve
Return the beef to the pan, toss until evenly coated, and cook for another 1–2 minutes.
Garnish with sliced green onions and sesame seeds.
Serving and Storage Tips
