Start by washing and peeling your Yukon Gold potatoes, then cut them into evenly sized chunks. Place the potatoes in a large pot and cover them with cold water. Bring it to a boil over high heat, then reduce to a simmer and cook for about 12 minutes. The potatoes should be fork-tender but hold their shape, then drain them in a colander.

While the potatoes are still warm, transfer them to a large mixing bowl. Toss the hot potatoes with apple cider vinegar right away; this will enhance their flavor. Allow them to sit for about 10 to 15 minutes for the vinegar to infuse into the potatoes.

In a separate bowl, whisk together the mayonnaise, Dijon mustard, sugar, salt, and pepper to create a smooth and creamy dressing. If you're adding pickle juice, mix it in now. Taste the dressing and adjust seasoning as needed.

Gently fold the dressing into the slightly warm potatoes until coated evenly. Add the chopped celery, onion, and fresh parsley, using a folding motion to keep potato chunks intact.

Cover the bowl with plastic wrap or a lid and refrigerate for at least one hour. For best results, let it chill overnight.