1.Combine ribs with remaining ingredients in a large non-metallic baking dish; season. Cover; refrigerate 3 hours or overnight.
2.Preheat oven to 180°C (160°C fan-forced). Drain ribs; reserve marinade. Place ribs on large oiled baking trays. Roast, uncovered, about 1 hour, turning once during cooking. Cover, stand 5 minutes.
3.To make olive and basil mash; boil, steam or microwave potatoes until tender; drain. Mash potatoes with butter and cream until smooth. Stir in olives and basil; season to taste.
4.Bring reserved marinade to the boil in a small saucepan; boil, uncovered, 3 minutes or until sauce is thickened slightly.
5.Cut ribs into pieces; serve with mash and sauce.