In a large bowl combine the cubed pork, soy sauce, sherry and cornflour. Leave for 20 minutes. Pour the oil into a wok or large frying pan. When it is quite hot, add the pork. Fry for 5-6 minutes or until golden. Remove the pork and pour off all but 2 tablespoons of the oil. Add the chopped garlic and fry for a few seconds. Add the remaining ingredients, fry for a few seconds to warn the spices through, then add the pork. Fry, stirring almost continuously, for a couple of minutes. Serve while hot and sizzling.