Cook potatoes in a large pot. Cool, peel, and cube. Place in large bowl and season with salt and pepper, if desired. Gently stir in onion and set aside.
In a medium skillet, fry bacon until crisp. Drain well on paper towels.
In the same skillet the bacon was cooked in, combine vinegar, sugar, water, cornstarch, and parsley. Stir constantly and bring mixture to a rolling boil.
Sprinkle bacon over potatoes, but do not stir. Pour hot sauce over all and gently stir in. Serve hot.
Note: Do not use flour instead of cornstarch for the thickener or the sauce will be “cloudy” instead of clear. You can adjust the amounts of sugar and vinegar to best suit your taste and add more or less bacon as desired.