Slice the beef into thin strips against the grain to ensure tenderness. Season with salt and black pepper. In a bowl, beat the egg and mix it with the beef until evenly coated. In a separate bowl, combine the cornstarch and flour, then coat each strip thoroughly. Allow the coated beef to rest for about 10 minutes so the coating adheres well before frying.

Heat vegetable oil in a deep pan to 350°F (175°C). Carefully fry the beef in small batches for 3 to 4 minutes until golden brown and crispy. Avoid overcrowding the pan, as this lowers the oil temperature and prevents the coating from becoming crunchy. Transfer the cooked beef to a wire rack to drain excess oil while maintaining its crispiness.

In a small bowl, whisk together the soy sauce, sweet chili sauce, ketchup, rice vinegar, brown sugar, minced garlic, grated ginger, and sesame oil until smooth. This sauce should have a balanced combination of sweetness, tanginess, and savory flavor that closely resembles the signature Panda Express version.

Heat one tablespoon of vegetable oil in a large wok or skillet over medium-high heat. Add the sliced onions and red bell peppers, then stir-fry for about 2 to 3 minutes. The vegetables should become slightly tender while still retaining a pleasant crunch and vibrant color.

Pour the prepared sauce into the wok with the vegetables and cook for about one minute until it begins to bubble and thicken slightly. Add the crispy fried beef and gently toss everything together until each piece is evenly coated in the glossy sauce. Sprinkle in the sliced green onions and stir briefly before removing the wok from the heat.

Transfer the Beijing Beef to a serving platter or individual bowls while it’s still hot. Garnish with freshly sliced green onions and a light sprinkle of sesame seeds for extra flavor and presentation. Serve immediately with steamed jasmine rice, fried rice, or chow mein to enjoy the crispy beef at its best. The glossy sweet-and-spicy sauce paired with crunchy vegetables makes every bite incredibly satisfying.