Make the sauce by combining the soy sauce, rice vinegar, sweet chilli sauce and sugar in a small jug or bowl.
Mix egg white with the soy sauce.
Place the cornflour/cornstarch and in another bowl and stir in the white pepper.
Place each piece of steak into the egg mixture then dredge in cornflour. (Note 6)
Place a frying pan on a medium to high heat and pour oil into a frying pan to around 1cm / ¼ inch deep.
Add the steak pieces when the oil is hot and steaming and fry for a minute of two on each side until they start to crisp up, then remove from the pan and set aside. Note that you may need to do this in two batches, depending on the size of your pan. (Note 7)
Carefully remove the excess oil from the pan or use a clean frying pan (you should be left with about a tablespoon. (Note 8)
Fry the onions unitl translucent, then add chilli, garlic and ginger and cook for 1-2 minutes until fragrant.
Pour in the sauce and let it reduce for a few seconds on a high heat before adding the crispy beef pieces.
Serve immediately, topped with spring onions/scallions and toasted sesame seeds.