Boil the potatoes (20 min):

1. Place unpeeled potatoes in a large pot of salted water. Bring to a boil and cook for about 20 minutes until tender but still firm.
2. → Test with a fork: It should slide in easily, but the potato shouldn't fall apart.

Prepare the onion:

1. While the potatoes cook, peel the white onion and finely dice it.

Cook onion in broth (3 min):

1. Cook onion in broth (3 min):
2. In a small saucepan, combine diced onion and vegetable broth. Bring to a boil and let simmer for 2–3 minutes until the onion is translucent.

Make the dressing:

1. In a bowl, whisk together vinegar, mustard, sugar, salt and pepper. Slowly stir in the hot onion-broth mixture. Finally, whisk in the oil.

Peel & slice the potatoes (while warm):

1. Peel the still-warm potatoes and cut into 0.5 cm (¼ inch) slices. Place them in a large salad bowl.

Add the dressing:

1. Pour the warm dressing over the potato slices. Gently fold everything together with a spatula, trying not to break the slices. The potatoes should absorb most of the liquid.

Let rest (30 min):

1. Let the salad sit at room temperature for at least 30 minutes so the flavors can meld. Stir gently once or twice during resting.

Taste & finish:

1. Before serving, adjust salt, pepper or add a splash of vinegar to taste. Sprinkle with fresh chives if desired.