Place the cubed potatoes in a large pot. Cover with cold, salted water by about an inch. Bring to a boil, then reduce heat and simmer until potatoes are fork-tender, about 15-20 minutes. Drain immediately and set aside to cool slightly.

While the potatoes cook, prepare the hard-boiled eggs. Peel and roughly chop the eggs once cooled. Set aside.

In a small bowl, whisk together all the dressing ingredients: mayonnaise, Dijon mustard, apple cider vinegar, sugar, salt, and pepper until smooth and well combined.

In a very large bowl, combine the slightly warm, drained potatoes, chopped hard-boiled eggs, celery, and red onion.

Pour the prepared dressing over the potato and egg mixture. Gently fold everything together using a rubber spatula until just combined, being careful not to mash the potatoes completely. Fold in the fresh dill.

Taste and adjust seasoning if necessary. Cover the salad and refrigerate for at least 2 hours, or preferably overnight, to allow the flavors to meld before serving.