Heat the oil in a flameproof casserole , add the onion and fry gently for 4 minutes until soft but not coloured.
Meanwhile, skin the root ginger and then crush the flesh with a mortar and pestle.
Add the crushed ginger to the casserole with the pork, increase the heat and fry until meat is browned on all sides.
Stir in the sherry and soy sauce, then the ginger ale, five-spice and seasoning to taste. Bring slowly to boiling point, stirring, then lower the heat, cover jand simmer for about 1 hour until the pork is just tender.
Add the stem ginger and pepper sliced to the asserole and continue cooking for a further 10 minutes. Serve hot.