Start by placing the diced Yukon Gold potatoes in a large pot and covering them with cold water. Bring to a boil, then simmer for about 12 minutes until fork-tender.

While the potatoes are still hot, drizzle in the apple cider vinegar and gently toss the potatoes.

In a separate bowl, whisk together the mayonnaise, Dijon mustard, sugar, salt, pepper, and optional pickle juice until smooth.

Add the diced celery, finely chopped onion, and fresh parsley to the cooled potatoes. Carefully pour the dressing over the mixture and fold gently.

Cover the bowl tightly and chill in the refrigerator for at least one hour before serving.