Wash the potatoes and boil them in salted water until soft.
In the meantime, peel and finely chop the onions.
Prepare the vinaigrette by making/heating up the broth, mixing in the vinegar, oil and mustard. Now place your chopped onions into the hot mixture, this will remove the bitterness from the onions.
Season the vinaigrette with sugar and salt to taste. (Be careful with the salt, because every broth has a different salt level. Add the salt to taste).
Peel the cooked potatoes and finley slice them.
Add the vinaigrette , bit by bit to the still-warm potatoes. In Swabia you want to achieve a wet, squelching consistency. In Swabia they speak of "schlotzing". The exact amount of vinaigrette needed will depend on the types of potatoes used.
Leave the salad to rest for about an hour, for the flavours to develop and the dressing to absorb. Ideally over night.
Just before serving sprinkle over some fresh chives or other herbs such as parsley or spring onions and adjust salt and pepper.
Serve at room temperature.