Boil potatoes until tender, then drain and cool slightly
Peel the potatoes if desired, then slice them
Cook chopped bacon in a skillet until crisp
Remove the bacon and leave some drippings in the pan
Add chopped onion to the drippings and cook until soft
Stir in vinegar, sugar, mustard, salt, and pepper
Add a little water or broth if needed
Pour the warm dressing over the sliced potatoes
Add the cooked bacon back in
Toss gently to coat
Stir in chopped parsley if desired
Serve warm or at room temperature