01 - Combine beef, soy sauce, Shaoxing wine, egg white, black pepper, and cornstarch in a bowl. Mix until the beef is thoroughly coated. Let marinate for 15 minutes.
02 - Whisk together all sauce ingredients in a small bowl and set aside.
03 - Heat vegetable oil to 350°F in a wok or deep pan. Fry beef strips in batches for 2 to 3 minutes until crisp and golden. Remove with a slotted spoon and drain on paper towels.
04 - Drain most of the oil, leaving 1 tablespoon in the pan. Add garlic, ginger, and chili if using, stir-fry for 30 seconds until fragrant.
05 - Add red bell pepper and stir-fry for 1 minute until slightly tender.
06 - Return crispy beef to the pan; pour in the prepared sauce. Toss quickly over high heat until beef is evenly coated and glossy, about 1 minute.
07 - Stir in spring onions briefly, then remove from heat. Serve immediately, garnished with toasted sesame seeds if desired.