Cook the potatoes in their skins in the salted water.
In the meantime, peel the cucumbers, halve or quarter lengthways depending on their thickness, core and cut into thin slices (approx. 2 - 3 mm). Don`t forget the bitter tasting!
Dice the bacon and fry in the oil. Peel the onions, dice them finely and add to the bacon. Let it become glassy. Pour in the stock and bring to the boil. Season to taste with vinegar, mustard, salt, pepper and sugar.
Drain the potatoes, peel them and cut them into slices while they are still hot. Put slices in the broth. Mix in the cucumber. Let it steep for 10 minutes on the lowest flame (cucumbers must still be crisp!). Let cool down.