Place the potato chunks in a large saucepan and cover them with cold, well-salted water. Bring the water to a boil, then reduce the heat to maintain a steady simmer.

Cook the potatoes for approximately 10-15 minutes, checking them with a fork near the end of cooking. They should be tender when pierced but still hold their shape instead of breaking apart.

Drain the potatoes thoroughly while they are still warm. Toss them gently with the apple-cider vinegar and a small pinch of salt, then let them cool until just warm or at room temperature.

In a separate bowl, whisk together the mayonnaise, sour cream, Dijon mustard, sugar, remaining kosher salt, and freshly ground black pepper. Continue whisking until the dressing is smooth and evenly combined.

Add the potatoes, chopped eggs, celery, red onion, and fresh dill or parsley to a large mixing bowl. Add the optional sweet-pickle relish or chopped dill pickles if desired.

Fold the dressing into the potato mixture gently, using a large spatula so the potato chunks and eggs remain intact. Stop mixing as soon as everything is coated.

Cover the bowl and refrigerate the potato salad for at least 1 hour, with 2-4 hours preferred for the fullest flavor. Taste it before serving and adjust the salt, pepper, mustard, or vinegar as needed.

Transfer the chilled salad to a serving bowl and finish with a light sprinkle of paprika and additional herbs. Keep it refrigerated until serving and return leftovers to the refrigerator promptly.