Combine the egg, salt, 2 tablespoons of the cornflour and 2 tablespoons of the rice wine in a bowl. Toss in the chicken and leave to marinate for 30 minutes.
Pour enough oil into the wok to deep-fry the chicken, and heat it to 190°C (375°F), or until a cube of bread dropped into the oil turns golden in 20 seconds. Drain the chicken and carefully lower half of it into the oil. Deep-fry for 2 minutes, until golden and crisp, then remove using a slotted spoon and drain on kitchen paper. Fry the rest of the chicken in the same way.
Pour the chicken stock into a wok over a high heat. Stir in the lemon juice, sugar and garlic, and the remaining cornflour and rice wine. Bring to the boil, then stir in the fried chicken. Cook, stirring, for 1–2 minutes, until the meat is coated in a velvety glaze, then stir in the sesame oil and cook for 1 more minute. Garnish with the lemon slices and spring onion strips.