Wash the potatoes and cook for about 20 minutes until almost done.
Meanwhile, peel and finely chop the onion. Bring diced onion to a boil in a saucepan with the beef broth.
Add vinegar, mustard, pepper and salt to soup and mix. Whisk in oil vigorously until a thick emulsion forms.
Drain the potatoes and let cool slightly.
Then peel and slice the potatoes and mix them in a bowl with the hot dressing.
Let stand for at least half an hour.
Preparation Tip:
The potato salad tastes better, the longer eh can pull.