In the first step, make a vinaigrette from vinegar and oil in a large bowl. Add vinegar and oil to the bowl, a little more oil than vinegar. Mix with a little hot meat stock with a whisk. Then add the chopped red onion and chives to the bowl. Season with plenty of salt and pepper. Mix everything together well.
Peel the cooked, still hot potatoes. Mash the soft potatoes well and add to the bowl. Mix everything together well.