Cook the baby yellow potatoes until fork-tender. Drain and let them steam-dry slightly so they hold the dressing beautifully.
In a small bowl, whisk together the miso paste, mustard, rice vinegar, and sesame oil until smooth and creamy.
While the potatoes are still warm, gently fold them into the miso dressing until evenly coated.
Toss in the chopped chives.
Sprinkle with furikake seasoning, if using.
Fold a small handful of crispy onions into the potato salad so there is crunch throughout.
Transfer the potato salad to a shallow serving bowl and top generously with extra fried onions.
Drizzle with any remaining dressing and let the toppings shine.