Wash the potatoes in cold water to remove any soil, giving them a gentle scrub if necessary, but leave on the fine skin. Cut any large potatoes in half. Bring a large pan of water to the boil and add a good pinch of salt. Lower in the potatoes and add mint sprigs, if you like, then simmer for 10-15 minutes or until just tender. Drain well and serve warm with the butter of your choice.