Boil the potatoes in salted water until tender, about 12–15 minutes. Drain, let them cool slightly, and slice into rounds.
Cook the bacon in a large skillet until crispy. Remove and set aside, leaving a little bacon fat in the pan.
Add the diced onion to the skillet and sauté for 3–4 minutes until soft and translucent.
Stir in the apple cider vinegar, Dijon mustard, sugar, salt, and black pepper. Cook for 1–2 minutes until the dressing is well combined.
Add the sliced potatoes to the skillet and gently toss to coat them in the warm dressing.
Return the chopped bacon to the pan and mix gently.
Serve warm, garnished with fresh parsley if desired.