Place potatoes in a large pot of salted water. Bring to a boil and cook until fork-tender but not falling apart. Drain and allow them to steam dry briefly.

In a bowl, whisk together mustard, mayonnaise, vinegar, olive oil, salt, and pepper. Add honey if you prefer a slightly rounded flavor. Taste and adjust acidity or seasoning.

Cut warm potatoes into bite-sized pieces. Lightly season with salt while still warm, which helps the potatoes absorb flavor.

Add potatoes to the dressing along with onion, celery, and herbs. Toss gently until coated evenly.

Let the salad rest for at least 15 minutes before serving. This allows flavors to settle and meld.