Boil the Potatoes: In a large pot of salted water, bring the potatoes to a boil. Cook until they are fork-tender, around 10-15 minutes. Drain them and let them cool before dicing.

Hard Boil the Eggs: In a separate pot, place your eggs and cover them with water. Bring to a boil, then turn off the heat and cover. Let sit for 9-12 minutes. Cool, peel, and chop the eggs.

Combine the Vegetables: In a large bowl, gently mix the diced potatoes, chopped eggs, pickle relish, diced onion, and chopped celery.

Make the Dressing: In a separate small bowl, whisk together the mayonnaise, mustard, salt, and pepper.

Mix: Pour the dressing over the potato mixture and stir gently until everything is well coated but not mushy.

Chill: Cover and refrigerate for at least an hour.