Tip the potatoes into a large pan and cook in boiling salted water for 10-15 mins until tender. While the potatoes are cooking, tip the wine, shallots and sugar into a saucepan, then boil for 10 mins until reduced by half. Tip in the vinegar and olive oil, then bring to the boil until the oil has become incorporated into the dressing. Pour half the dressing over the warm potatoes and leave to cool. Stir through the remaining dressing and parsley before serving.