Cut the pork shoulder into 2.5-centimetre cubes. In a bowl, combine the soy sauce, rice wine or dry sherry, sesame
oil, salt, pepper and ½ teaspoon sugar. Give it a mix, then add the pork and marinate for 10 minutes.
In another bowl, combine the flour and ½ cup cornflour. Drain the pork, reserving the marinade. Lightly dredge the pork pieces in the flour/cornflour mixture and set them aside on a plate.
Drain the pineapple chunks, reserving ½ cup of the juice. In a bowl, stir together the juice, tomato sauce, vinegar, 2 tablespoons sugar, 1 tablespoon cornflour and the reserved marinade.
Heat 1 cup of oil in a large flat-bottom wok until it’s hot but not smoking. Add half the pork, spreading the pieces around in the oil. Cook 1-2 minutes until they begin to brown, and then turn them. After 3-4 minutes, when they’re brown on all sides, transfer them to a plate lined with paper towel. Repeat with rest of the pork.
Wash and dry the wok and return it to high heat. Add the remaining 1 tablespoon oil and the ginger, and stir-fry 10 seconds. Add the green capsicum and stir-fry one minute. Add the reserved pineapple chunks and swirl the sweet-and-sour sauce into the wok.Bring the mixture to a boil, stirring until it’s just thickened, about one minute. Add the pork and cook, stirring, for 2-3 minutes.