To make the beef and marinade, mix the soy sauce, sherry, tangerine juice, garlic, sesame oil and chilli flakes in a shallow tray to make the marinade.
Thinly slice the steak and place in the marinade. Cover and refrigerate for 2 hours. Drain well.
Preheat a deep-fat fryer to 180C. (CAUTION: hot oil can be dangerous. Do not leave unattended.) Dredge the beef in the cornflour, then deep-fry until crisp. Carefully remove from the fryer and drain on kitchen paper.
To make the sauce, heat the oil and fry the shallot. Add the ginger and garlic and cook for 1 minute. Add the star anise, sugar and tangerine peel, then stir in the soy sauce, tangerine juice and cornflour. Simmer until thickened.
Add the beef and stir. Sprinkle on the spring onions and tangerine segments to serve.