Boil the potatoes in a large pot of salted water until tender, then drain and let them cool slightly before peeling and dicing them.

In a very large mixing bowl, combine the diced potatoes, mayonnaise, chopped celery, and finely chopped red onion.

Add the Dijon mustard, apple cider vinegar, salt, and black pepper to the potato mixture and stir gently to combine all ingredients well.

Taste the potato salad and adjust the seasonings as needed, adding more salt, pepper, or mustard to suit your preference.

Cover the bowl and refrigerate the potato salad for at least one hour before serving to allow the flavors to meld.