I just asked my father 'bout the details, here they are:

-cooked potatos, sliced, have to be still hot/warm, so they soak up the vinaigrette
-vinaigrette (two parts oil, one part whitewine vinegar, salt, pepper, garlic)
-onions
-chives

mix all these ingredients then:

-some some grinded nutmeg and
-a cup of hot broth (made of a stock cube)

on top, then mix again, voilą...