Place the peeled and cubed potatoes in a large pot and cover with cold water by 1 inch. Add 1 teaspoon of salt to the water.
Bring the water to a boil over medium-high heat and cook the potatoes until tender but still firm, about 10-12 minutes. Drain and set aside.
While the potatoes are cooking, place the eggs in a saucepan and cover with cold water by 1 inch.
Bring to a boil over medium heat. Once boiling, remove from heat, cover, and let sit for 12 minutes.
Drain the hot water from the eggs and transfer them to a bowl of ice water. Let cool for 5 minutes, then peel and chop the eggs.
In a large mixing bowl, whisk together the mayonnaise, sour cream, Dijon mustard, apple cider vinegar, granulated sugar, salt, and black pepper until smooth.
Add the warm potatoes, chopped eggs, celery, and onion to the dressing. Gently fold to combine, ensuring the potatoes remain intact.
Sprinkle the chopped fresh parsley over the salad and gently mix in.
Serve the potato salad warm or at room temperature.