Cut potatoes into 1-inch chunks (no need to peel Yukon Golds—their thin skin adds texture and nutrients). Dice celery into 1/4-inch pieces and finely mince onion so it distributes evenly throughout the dressing. Chop chives and dill and set aside. Measure out sour cream, mayonnaise, mustard, and all seasonings into separate small bowls. Bring a large pot of salted water to a boil, then add the potato chunks and cook for 10-15 minutes until they're fork-tender but not falling apart.

While potatoes cook, whisk together sour cream, mayonnaise, and Dijon mustard in a medium bowl until smooth. Add both measurements of apple cider vinegar (you'll use 1 tablespoon total from the two separate amounts listed), then season with celery salt, salt, pepper, and garlic powder. Whisk until fully combined and taste to adjust seasonings—I like to add a tiny pinch more celery salt since it's the backbone of the flavor. Set dressing aside.

Drain the cooked potatoes thoroughly and transfer them to a large mixing bowl while still warm. This is important—warm potatoes will absorb the vinegar and dressing flavors better than cold ones. Add the celery, minced onion, chives, and dill to the warm potatoes and gently toss to combine. Pour the creamy dressing from Step 2 over the potato mixture and fold everything together gently with a rubber spatula until all potatoes are evenly coated. Serve warm or refrigerate until ready to serve.