Rolled roast pork loin with apple and chestnuts

Name: Rolled roast pork loin with apple and chestnuts
Prep time: 20 min
Cook time: 1 h
Total time: 1 h 20 min
Cuisine: Australian
Ingredients: 1.8 kg piece of pork loin; 1 tbsp olive oil; 3 small pink lady apples, unpeeled, halved horizontally; 200 gm peeled chestnuts (see note); 12 shallots; ½ cup (loosely packed) sage leaves; 350 ml dry cider; Apple and sage stuffing; 20 ml olive oil; 10 gm butter; 4 shallots, finely chopped; 4 pink lady apples, unpeeled, coarsely chopped; 125 ml dry cider; 50 ml cider vinegar; 20 gm caster sugar; 2 tbsp coarsely torn sage leaves