Place the quartered potatoes in a large pot and cover with cold, salted water. Bring to a boil and cook until fork-tender, about 15-20 minutes. Drain immediately and allow the potatoes to cool slightly.

While the potatoes are cooling, prepare the dressing: In a medium bowl, whisk together the mayonnaise, sour cream, Dijon mustard, lemon juice, and lemon zest until well combined.

Stir the fresh dill, salt, and pepper into the dressing mixture. Taste and adjust seasoning as necessary.

In a very large bowl, gently combine the slightly warm (or fully cooled) potatoes with the chopped celery, minced red onion, and chopped hard-boiled eggs.

Pour the creamy dill dressing over the potato mixture. Fold gently but thoroughly until everything is coated evenly, taking care not to mash the potatoes too much.

Cover the potato salad and refrigerate for at least 2 hours (preferably 4 hours) before serving to allow the flavors to meld.