1) Cut the lamb into thin slices. 2) Marinate the slices in 2tbsp of the cornflour and crushed black bean sauce for about 10 minutes. 3) Heat the rapeseed oil in a wok or saucepan and deep-fry the lamb slices for about 20 seconds, stirring to separate each piece. 4) When the slices are lightly coloured, remove with a perforated spoon and drain. 5) Pour off the excess oil, leaving about a tablespoon, add the ginger root, soy sauce, sherry, vinegar, sugar and remaining cornflour. Stir for about 1 minute. 6) Add the lamb slices and sesame oil and stir briefly before serving.