Sticky ribs with roast potato salad

Name: Sticky ribs with roast potato salad
Ingredients: 3 racks pork spare ribs, or about 1½ kg/3lb 5oz single pork spare ribs; 1 small onion, diced; 1 tbsp olive oil; 1 garlic clove, crushed; 2 tbsp smoked paprika; 1 tsp mild chilli powder; 300ml tomato passata; 2 tbsp tomato purée; 150ml cider, white or red wine vinegar; 125g dark muscovado sugar; 1½ kg new potatoes, skin on; 2 tbsp olive oil; 1-2 rosemary sprigs, finely chopped, or a pinch of mixed dried herbs; 2 tbsp white or red wine vinegar