Boil the potatoes. Finely dice the onion and bacon and sauté until translucent. Dice the bacon and leave it out. Dice the cucumber. Mix everything together carefully.
Prepare a light roux with a little butter and the flour. Deglaze immediately with vinegar and cucumber stock. Add the cream and sour cream, as well as salt and pepper from the mill. Add the sugar. Stir and mix with the finely diced ingredients. Put aside.
Peel the warm jacket potatoes and cut into fine slices. I do this with the egg slicer. Pour the marinade over it and fold in carefully. Let it steep for 30 minutes.