Boil the potatoes and let cool down.
Heat up the vegetable broth.
Add the mustard, vinegar, sunflower oil, salt and pepper. Mix well.
Peel and cut the onion in small pieces.
Cut the cornichons, chives, and parsley.
Add the onion, cornichons, chives and parsley in the broth.
Cut the potatoes in slices, and add the broth on top. Mix and let rest 30 minutes.