Peel and dice the carrots and potatoes. Cut and dice the smoked pork loin.
Bring water to a boil. Add onion, garlic and beef soup. Let simmer for 20 minutes. Then take out the onion and garlic and add the meat. Pre-cook the Kassler 10 minutes. Then add the carrots and the tied parsley and cook for another 5 minutes. Now add the potatoes and tarragon to the soup. Let cook for another 10 minutes. Then take the parsley out again.
When the vegetables are done, remove the saucepan from the stove.
Heat oil in a pot. When the oil is hot, add the flour and sauté for 2 minutes, then set the saucepan aside and let it cool. Now dissolve the mass with a cup of water. Stir until there are no more lumps. Add the cream, egg yolk and sour cream and stir everything well.
Now dissolve the roux with 2 tablespoons of the soup. Then pour the dissolved roux back into the soup. Then season the soup with 3 - 4 tablespoons of vinegar (depending on your taste). Use salt only when needed.
Finally let everything simmer again for 2 minutes.