Wash and scrub the potatoes.
Place potatoes in a pot and add water to cover by 1 inch. Bring to a boil. Add salt. Turn the heat down and allow the potatoes to simmer until they're tender (you should be able to poke the potatoes with a fork).
Add vinaigrette ingredients to a small bowl and whisk until well-combined.
When the potatoes are ready, remove from heat and drain well. Place them in a large mixing bowl and immediately dress them with the Dijon mustard dressing. Gently toss to coat.
Add onions, fresh herbs, and capers. Toss gently to combine.
Transfer the potatoes to a serving platter. For best results, allow the potato salad some time to marinade before serving.
You can refrigerate it for 1 hour or so but be sure to bring it to room temperature before serving.