Submerge the potato cubes in a large pot of cold, salted water. Bring to a boil and cook for roughly 8–10 minutes. You want them tender enough to pierce with a fork, but firm enough that they don't crumble. Drain thoroughly and let them air-dry for 5 minutes so the excess steam escapes.

In a small mixing bowl, whisk together the mayonnaise, mustard, apple cider vinegar, and sugar. Stir in the celery salt and black pepper until the dressing is completely smooth and pale yellow.

Place the warm potatoes in an oversized bowl. Pour half of the dressing over them while they are still warm; this allows the potatoes to absorb the vinegar and mustard flavors more deeply.

Add the diced hard-boiled eggs, sweet relish, and sliced scallions. Pour the remaining dressing over the top. Using a large wooden spoon or spatula, gently fold the ingredients together. If you prefer a "smashed" style, you can stir more vigorously to break down some of the potato edges.

Cover the bowl tightly and refrigerate for at least 4 hours. Potato salad is a dish that truly transforms as it sits, allowing the starches to marry with the creamy dressing.

Just before placing on the table, give it one last light toss and sprinkle the surface with smoked paprika for a hint of color and woodsy aroma.