First make the sauce. Put all the ingredients into a small pan, simmer for a couple of minutes until thickened, then set aside.
Cut the beef into strips, 3–4mm thick. Heat a 2–3cm depth of oil in a wok or a deep saucepan – the fat will bubble up when you add the beef, so don’t use a shallow pan. Heat the oil to 180°C, or until a cube of dry white bread dropped in turns golden in just under a minute.
Sift the cornflour and five-spice powder, if using, onto a plate. Toss the beef strips in the cornflour until well coated on all sides.
Fry the beef in a couple of batches to avoid crowding the pan. Lower into the hot oil and fry until golden and crisp, which should only take a couple of minutes. Scoop out with a slotted spoon and place on kitchen paper to drain. Let the oil come back up to temperature before adding the second batch of meat to the pan.
Mix the orange zest with the flaky sea salt and sprinkle over the beef.
For the salad, toss the vegetables together with the rice wine vinegar.
Pile the salad and crispy beef onto individual plates. Trickle on the sauce and add a scattering of sesame seeds. Garnish with coriander if you have some to hand.
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