Wash the potatoes and cook with the skin on until they are cooked through but still firm. Mix the hot broth with the vinegar, horseradish and oil.
Drain the potatoes, leave to cool a little, then peel and cut into thin slices, immediately add to the marinade. Season with pepper, cover and let steep.
Finely dice the bacon and fry until translucent. Finely dice the onion and add to the bacon. Mix the onion and bacon mixture into the potato salad. Just before serving, mix in the washed, finely chopped endive salad. If necessary, season again to taste.