In a large cast-iron Dutch oven, bring potatoes and water to cover by 2 inches to a boil over medium-high heat. Reduce heat, and simmer until fork-tender, about 10 minutes. Drain well.
In a large bowl, mash together egg yolks with a fork until crumbly; stir in mayonnaise, mustard, 1 tablespoon water, vinegar, salt, ¼ teaspoon pepper, and paprika until smooth.
Coarsely chop egg whites. Gently stir potatoes, celery, onion, relish, and egg whites into mayonnaise mixture until well coated. Cover and refrigerate for up to 24 hours before serving. Just before serving, sprinkle with remaining ¼ teaspoon pepper; garnish with chives, if desired.
Recipe by Southern Cast Iron at https://southerncastiron.com/deviled-egg-potato-salad/