Put potatoes in a large pot and add cold water to cover. Bring to a simmer over medium heat and cook until just tender.Advertisement
Drain the potatoes. When cool enough to handle, cut the potatoes into large dice and gently toss them with 2 tablespoons of the vinegar in a large bowl. Let cool to room temperature.
Whisk mayonnaise, sour cream, mustard and the remaining 2 tablespoons vinegar in a bowl. Season with salt and pepper.
Add the dressing to the potatoes. Add onions, celery and parsley and toss gently to combine.
1 1/2 starch, 1/2 vegetable, 1 fat