Step 1: In a medium bowl, combine the thinly sliced flank steak with 1 tablespoon of soy sauce, 1 tablespoon of cornstarch, and 1 teaspoon of sesame oil. Mix well to coat the beef evenly. Set aside to marinate for at least 15 minutes while you prepare the vegetables and sauce.
Step 2: In a small bowl, whisk together the remaining 3 tablespoons of soy sauce, rice vinegar, brown sugar, beef broth, and the remaining 1 tablespoon of cornstarch until smooth. This is your savory pepper steak recipe sauce. Set aside.
Step 3: Heat 1 tablespoon of vegetable oil in a large skillet or wok over medium-high heat. Add the marinated beef in a single layer and cook for 2-3 minutes per side, until browned. Do not overcrowd the pan; cook in batches if necessary. Remove the cooked beef from the skillet and set aside.
Step 4: Add the remaining 1 tablespoon of vegetable oil to the same skillet. Add the sliced yellow onion, green, red, and yellow bell peppers. Sauté for 3-5 minutes, stirring frequently, until the vegetables are crisp-tender. You want them to retain a slight crunch for the best pepper steak recipe texture.
Step 5: Push the vegetables to one side of the skillet. Add the minced garlic and grated ginger to the empty space and cook for 30 seconds until fragrant, being careful not to burn them.
Step 6: Return the cooked beef to the skillet with the vegetables. Give the prepared sauce a quick whisk again (as cornstarch can settle) and pour it over the beef and vegetables. Bring the mixture to a simmer, stirring constantly, until the sauce thickens and becomes glossy, about 1-2 minutes.
Step 7: Remove the skillet from the heat. Serve the classic pepper steak recipe immediately over freshly cooked white rice. Garnish with sesame seeds or chopped green onions if desired. Enjoy your homemade pepper steak recipe!