- Step 1: Cook the Potatoes: Place the cubed potatoes in a large pot and cover with cold water. Add a pinch of salt. Bring to a boil and cook until the potatoes are tender but not mushy, about 12-15 minutes. Drain the potatoes and let them cool slightly. 
- Step 2: Hard-Boil the Eggs: While the potatoes are cooking, place the eggs in a separate saucepan and cover with cold water. Bring to a boil, then remove from heat, cover, and let sit for 10 minutes. Transfer the eggs to an ice bath to stop the cooking process. Peel the eggs and chop them coarsely. 
- Step 3: Prepare the Dressing: In a large bowl, whisk together the mayonnaise, Dijon mustard, and apple cider vinegar until smooth. 
- Step 4: Combine Ingredients: Gently fold the slightly cooled potatoes, chopped eggs, celery, red onion, and parsley into the dressing. Be careful not to mash the potatoes. 
- Step 5: Season and Chill: Season the salad with salt and freshly ground black pepper to taste. Cover and refrigerate for at least 2 hours, or preferably overnight, to allow the flavors to meld. 
- Step 6: Serve: Before serving, give the salad a gentle stir. Garnish with additional fresh parsley, if desired. Serve cold.
Optional: For a tangier flavor, add a tablespoon of sweet pickle relish to the dressing. Chopped bacon can also be added for a smoky flavor. For a lighter dressing, use half mayonnaise and half plain Greek yogurt.