1.Preheat oven to 240°C/220°C fan-forced. Place pork in large baking dish; rub scored rind with salt. Roast pork, uncovered, 25 minutes or until rind blisters. Drain excess fat from dish.
2.Reduce oven temperature to 180°C/160°C fan-forced. Add onions and celery to baking dish with pork. Roast pork and vegetables for a further 45 minutes or until cooked through. Turn or shake vegetables occasionally during cooking.
3.Meanwhile, make apple and cider sauce; heat butter in medium saucepan; cook shallots, stirring, until softened. Add apple; cook, stirring, 2 minutes. Add cider; bring to the boil. Boil, uncovered, 1 minute. Cover, simmer, 5 to 10 minutes or until apples are tender and cider has reduced slightly. Stir in sugar, juice and salt. Blend or process apple mixture until smooth.
4.Remove pork and vegetables from oven. Cover with foil; stand pork 10 minutes before slicing. Remove vegetables from dish, toss with parsley.
5.Serve pork with sauce and vegetable mixture.
Use a Stanley knife to score the rind, 1cm apart, across the pork in the same direction as you will slice. The rind should be scored deeply, through to the fat, to ensure the fat is rendered and the crackling will be crisp. Alternatively, ask your butcher to do this for you.