Put the chicken, egg and sea salt in a bowl, toss together and leave for 20 minutes.
Remove the chicken from the egg, allowing the excess to drip away, and toss in the cornflour until evenly coated. Heat the oil in a wok or deep-fryer until just smoking (180°C/350°F), and deep-fry the chicken pieces until golden brown and cooked through, then drain on paper towel.
Finely grate the zest from half a lemon, then juice the whole lemon. Peel and fillet the other lemon. Put the sugar, vinegar,