Peel potatoes. Peel the onions and cut into strips. Dice the bacon.
Put some oil in a pan and heat it up well. Cut the potatoes into thin slices with the knife above the pan and fry them - turning occasionally. Then add the onions and bacon directly. Fry everything briefly (approx. 4 minutes) until the potatoes and onions have taken a little color. Turn the heat down to half. Now add the butter, salt and a good amount of pepper and turn briefly. Put a lid on the pan and cook with the lid on for about 5 minutes (only turn occasionally). Then remove the cover. Briefly turn up the heat to full and fry the potatoes again briefly. Serve hot.