1 medium dill pickle, finely chopped (about 1/3 cup)
2 hard-boiled eggs, peeled and chopped, optional
1/4 cup chopped fresh chives
Salt and freshly ground black pepper
Bring a large pot of water to a boil. Add the cubed potatoes and boil for 15-20 minutes.
Meanwhile, set up an ice bath. Add cold water to a medium bowl filled with ice. Drain the potatoes and add to the ice bath.
In a large bowl, sprinkle the vinegar over the potatoes and lightly season with salt.
Add onions to a small bowl and cover with warm water. Wait 10 minutes then rinse. (This tones down the raw flavor of the onions).
Combine sour cream, mayonnaise and the mustard in a bowl. Whisk until smooth.
Add sour cream mixture, onion, celery, pickles, eggs, and chives to the potatoes. Gently stir to combine. (Try not to mash the potatoes). Season with salt and pepper to taste. Refrigerate at least 30 minutes before serving.