Scrub, peel, and cut potatoes into one-inch cubes. Place in a large pot, cover with water, and boil for 10 minutes until firm-tender. Drain and cool.
Chop cooled potatoes, onions, and celery, and place in a large mixing bowl.
Hard-boil eggs, cool, peel, and chop or press through a cooling rack into the potato mixture.
Mix mayonnaise, mustard, vinegar, pickle relish, salt, and pepper in a bowl.
Pour the dressing over the potato mixture, stir gently, and sprinkle with paprika and spring onions. Refrigerate for at least 30 minutes before serving.
Notes
Let the salad chill in the refrigerator for at least 30 minutes to allow flavors to meld.