Dice the onions. Heat oil. Sauté onions until translucent.
Peel potatoes, cut potatoes and beet into cubes, add both to onions and fry.
Prepare a marinade from the ingredients listed, add to the potato mixture and bring to the boil.
Cut the frisée salad into strips and arrange on plates. Cool the potato salad a little bit and spread it evenly on top.