Step 1: Place the potatoes in a large pot and cover with salted water. Bring to a boil and cook for 15-20 minutes until fork-tender.
Step 2: While potatoes cook, fry the diced bacon in a large skillet over medium heat until crispy. Use a slotted spoon to remove bacon to a paper towel, leaving the fat in the pan.
Step 3: Add the diced red onion to the bacon fat and sauté for 3-4 minutes until softened and translucent.
Step 4: Whisk in the apple cider vinegar, water, Dijon mustard, sugar, salt, and pepper. Bring to a simmer for 1-2 minutes until slightly thickened.
Step 5: Drain the cooked potatoes. While still warm, peel (optional) and slice them into 1/4 inch rounds.
Step 6: Pour the warm dressing over the potato slices and gently toss to coat. Fold in the crispy bacon and fresh parsley before serving.