In a mixing bowl, combine 360g of thin-cut sirloin steak with 1 small egg, 4 tablespoons of cornflour, ¼ teaspoon salt, ¼ teaspoon black pepper, and ⅛ teaspoon white pepper. Mix well to coat beef evenly.

Heat 3 tablespoons of sunflower oil in a non-stick frying pan over high heat. Fry the beef strips in batches for 5-6 minutes until dark brown and crispy. Let drain on kitchen paper.

In the same pan, add remaining 1½ tablespoons of oil over medium heat. Sauté sliced onion for 2 minutes. Add red chili, ginger, and garlic, cooking for another 30 seconds.

Pour in rice vinegar, dark soy sauce, tomato puree, caster sugar, tomato ketchup, and sweet chili sauce. Stir and let bubble for 2-3 minutes until thickened.

Fold the crispy beef strips back into the sauce, warm through for 1-2 minutes, then serve hot over steamed jasmine rice or stir-fried noodles.