To cook the potatoes
Cook the potatoes (uncovered) in salted water over a medium heat for approx. 25 mins. until just soft. Drain the potatoes, peel while hot, cut into slices approx. 5 mm thick.
In a bowl, mix the mustard with all the other ingredients up to and including the garlic, season. Mix in the potatoes, cover and leave to stand at room temperature for approx. 1 hr. Mix in the chives.