Wash and peel the potatoes if desired, then cut them into evenly sized cubes.
Place the potato cubes in a large pot and cover with water.
Bring the water to a boil over medium-high heat.
Reduce the heat and simmer for 15-20 minutes until the potatoes are tender.
Drain the potatoes and let them cool slightly.
In a large mixing bowl, combine mayonnaise, Dijon mustard, and apple cider vinegar.
Add diced celery, red onion, and sweet pickle relish to the dressing.
Gently fold in the cooled potatoes until well coated.
Season with salt and pepper to taste, and garnish with fresh parsley.
Chill the salad for at least an hour before serving for best flavor.