Cook for 10–15 minutes until tender but still firm.

Drain the potatoes and allow them to cool slightly.

In a bowl, whisk together mayonnaise, Dijon mustard, vinegar, salt, and pepper.

In a large mixing bowl, combine potatoes, celery, and red onion.

Pour the dressing over the mixture and gently fold until evenly coated.

Stir in chopped parsley and adjust seasoning if needed.

Refrigerate for at least 1 hour before serving.