Preheat oven to 250°C. Line a baking dish with baking paper.
Add onion, cut-side down, into dish, then place a wire rack over dish.
Pat pork skin dry with paper towel and tie with cooking twine (optional). Place pork on rack, drizzle with half the oil and sprinkle with salt. Bake for 45 minutes or until crackling forms.
Reduce heat to 200°C and bake for a further 30 minutes. Add apple and sage and drizzle with remaining oil. Cook for a further 30 minutes or until pork is cooked and rind is crisp. Stand, loosely covered, for 15 minutes before slicing. Serve with apple, onion, sage and Baked cabbage with creamy mustard sauce (see tip).
