Parboil the potatoes for about 5 to 10 minutes. Drain the water and place the potatoes in an oven tray. Drizzle with olive oil and season with salt and pepper, then bake for 30 minutes. Add the onion and balsamic vinegar and bake for a further 30 minutes.
Make the dressing by chopping all the herbs, then combining with the rest of the ingredients listed. Whisk well. Once potatoes are done, remove from oven and immediately add to dressing. Give it a gentle stir and garnish with fresh chives.
Serve with roast meat of choice and a fresh green salad.