Cut the sorrel into small pieces. Fry the onion or shallot in butter or a little oil until translucent. Add sorrel, dust with flour and deglaze with a sip of white wine or apple cider vinegar. Add the broth. Add the potato cubes if you like. Simmer for about 15-20 minutes. Finally add the crème fraiche.
For the variant without potatoes, now add toasted bread cubes or oat flakes. Decorate with some flowers if necessary.