Cook the potatoes in water. Drain the water away and let them cool down to room temperature.
Heat up the vegetable broth in a casserole.
Peel and cut the red onion in small pieces.
Mix the broth with the oil, vinegar, mustard, and the spices.
Cut the potatoes in slices and pour the broth mixture over them. Mix well.
Let it soak in and stir together a few times during the next 15 minutes.