Boil potatoes until tender, then peel and cut into 3cm
pieces; set aside.
Fry bacon gently in a large frying pan, stirring
occasionally, until crisp. Use a slotted spoon to remove bacon
from pan, retaining the fat in the pan, and drain bacon on
absorbent paper.
Combine sour cream, mustards, vinegar and a pinch of salt;
add to pan with the bacon and stir to mix. Quickly add potato,
lifting and stirring. Season with pepper, if desired. Transfer
to a serving bowl and cool to room temperature. Serve
sprinkled with the chives and freshly ground black pepper, if
desired.