Cut mini potatoes in half and place in a large pot. Cover potatoes with cold water, covering by 3-4 inches, at least. Generously salt the water. Bring to a boil. Boil potatoes until just tender. Test by piercing potatoes with the tip of a sharp knife. The potatoes are done when the knife passes through the potato without resistance.
Drain potatoes well and place in a large bowl.
Make the Vinaigrette: In a medium bowl, stir together the vinegar and Dijon mustard. Using a whisk, slowly add the olive oil in a slow stream, whisking well while adding, until it is all added. Pour over the still warm potatoes and toss well to combine. Add the sliced red onion and toss to combine. *Note: if you'd like the red onion fresh and crisp, save until the potatoes are cool and add it with the fresh herbs. Cover and refrigerate until cool, about 2 hours.
Once the potatoes are cold and before serving, toss the salad with the sliced red onion and chopped herbs and generously season with salt and freshly ground pepper.