01 - Place the potatoes in a large pot and cover with cold salted water. Bring to a boil, then reduce to a simmer and cook until fork-tender, about 10–12 minutes. Drain and let cool slightly.
02 - In a large bowl, whisk together mayonnaise, sour cream, Dijon mustard, apple cider vinegar, salt, pepper, and sugar until smooth.
03 - Add the cooled potatoes, celery, red onion, eggs, parsley, and pickles (if using) to the dressing. Gently fold until everything is well coated.
04 - Taste and adjust seasoning as needed. Cover and refrigerate for at least 1 hour before serving to allow flavors to meld.
05 - Serve chilled or at cool room temperature, garnished with extra parsley if desired.