Wash and peel the potatoes if desired. Cut into 1-inch chunks and place in a large pot of cold salted water.

Bring to a boil over high heat, then reduce to medium and cook for 10-15 minutes until fork-tender. Drain and cool.

In a bowl, mix mayonnaise, mustard, salt, and pepper until smooth.

In a large bowl, combine cooled potatoes, celery, pickles, and onion. Gently fold in the dressing until evenly coated.

Chill for at least an hour before serving to allow flavors to meld.