Boil the potatoes in salted water. When the potatoes are done, they are mashed or chopped with the help of a food processor.
Cut the lettuce into thin strips and finely dice the onions. Make a dressing with vinegar, salt, pepper and water and add to the salad.
Fry the diced bacon until crispy. Then put the butter in the pan and let it melt. Add the flour and add cold water while stirring. Stir until the sauce is nice and creamy.
Now put the salad on the potatoes, pour the bacon sauce over it and stir everything thoroughly.