Beef in Oyster Sauce

Name: Beef in Oyster Sauce
Prep time: 20 min
Cook time: 10 min
Total time: 30 min
Yield: 4
Ingredients: Ingredients; 1 lb beef sirloin or flank steak, thinly sliced against the grain; 2 tablespoons cornstarch; 2 tablespoons soy sauce, divided; 1 tablespoon Shaoxing wine or dry sherry; 3 tablespoons vegetable oil, divided; 4 cloves garlic, minced; 1 tablespoon fresh ginger, minced; 1 medium onion, sliced; 1 red bell pepper, sliced; 1 green bell pepper, sliced; 4 shiitake mushrooms, sliced (optional); 2 green onions, cut into 2-inch pieces; 1 tablespoon sesame seeds for garnish; Sauce; 4 tablespoons oyster sauce; 2 tablespoons soy sauce; 1 tablespoon dark soy sauce (for color); 1 teaspoon sugar; 1 teaspoon sesame oil; 1/4 cup beef broth or water; 1 teaspoon cornstarch