Preheat oven to 425°F (220°C). Toss the quartered potatoes with olive oil, salt, and pepper until evenly coated.

Spread the seasoned potatoes in a single layer on a large baking sheet. Roast for 35-45 minutes, turning halfway through, until the potatoes are tender on the inside and deeply golden brown and crispy on the edges.

While potatoes are roasting, prepare the dressing. In a medium bowl, whisk together the mayonnaise, Dijon mustard, apple cider vinegar, and celery seed until completely smooth.

Once the crispy potatoes are finished roasting, remove them from the oven and immediately transfer them to a large bowl. While they are still warm, gently pour about two-thirds of the dressing mixture over the potatoes and toss lightly to coat.

Allow the potatoes to cool slightly (about 15 minutes). Then, fold in the diced celery, minced red onion, chopped fresh dill, and chopped hard-boiled eggs.

Taste the salad and add the remaining dressing if a creamier consistency is desired. Adjust salt and pepper as needed. Chill for at least 1 hour before serving for the best flavor integration.