Combine sake, sugar, soy sauce and ginger in a bowl and stir until sugar dissolves.
Add sliced pork and marinade 10 min's (do not marinate longer than 10 min's as pork will become tough.) Drain pork over a small bowl, reserve marinade.
While pork is marinating, remove thick ribs from cabbage (the thick white stalky part in the centre.) Cut leaves into approx 4cm squares.
Heat the oil in a wok or large frying pan, add pork stir-fry for about 5 Min's or until pork is almost cooked. Add reserved marinade stir-fry for a couple of minutes, finally add cabbage and stir-fry until cabbage just wilts.