In a mixing bowl, add the thin-cut sirloin steaks and crack one egg over them, tossing until the beef is evenly coated. Gradually sprinkle in cornflour, salt, black pepper, and white pepper, ensuring each piece is well covered with the mixture. Let this sit for a few minutes while you prepare your cooking station.

In a large frying pan, pour in about 3 tablespoons of sunflower oil and heat it over medium-high heat. The oil is ready when you see it shimmering but not smoking.

Carefully add the beef strips to the hot oil in batches, frying each batch for 5-6 minutes until they are dark brown and crispy. Remove the beef and place it on paper towels to drain excess oil.

In the same frying pan, add a splash more oil if needed, and toss in the chopped onion. Sauté for about 2 minutes until the onions just begin to soften, then add in the chopped red chilli, minced ginger, and minced garlic.

Pour in the rice vinegar, dark soy sauce, tomato puree, caster sugar, tomato ketchup, and sweet chilli sauce to the pan and stir well. Bring to a gentle simmer for 2-3 minutes.

Return the crispy beef back into the pan, stirring gently to coat each piece thoroughly with the luscious sauce. Heat everything together for 1-2 minutes until warmed through and glistening with sauce.