Place the quartered potatoes in a large pot and cover with cold, salted water by about an inch. Bring to a boil over high heat.

Reduce heat to a simmer and cook for 15-20 minutes, or until potatoes are fork-tender. Drain thoroughly and let the potatoes cool slightly (about 10 minutes).

While potatoes are cooling, prepare the vinaigrette: In a small bowl, whisk together the apple cider vinegar, olive oil, Dijon mustard, sugar, salt, and pepper until emulsified.

While the potatoes are still warm, gently transfer them to a large mixing bowl. Pour about half of the vinaigrette over the warm potatoes and toss gently to coat. The warmth helps the potatoes absorb the dressing.

Add the diced celery, minced red onion, and chopped fresh dill to the bowl. Toss everything together, adding more vinaigrette as needed until the salad is lightly coated but not swimming in dressing.

Taste and adjust seasoning with extra salt or pepper if necessary. Cover and refrigerate for at least 1 hour before serving to allow the flavors to meld. Serve chilled or at room temperature.