Bring the vinegar, water and salt to the boil, add the soup greens and spices and allow to cool. Wash the roast beef and pour the stock over it. Soak in it for 4-6 days and turn daily.
Remove the meat, dab it off, sear it, fry the soup greens (fresh, not the one pickled with the meat) and add about 1/2 l of the stock. Add the sauce to taste, it should be around 100-200 ml so that the sauce is also sour. Cook for about 2 hours or until the meat is tender. Remove the meat from the broth and cut into slices.
For the sauce, either roast the flour in fat and deglaze with the broth or puree the soup greens and bind the sauce with it or use a sauce thickener and add sour cream.
We also have spaetzle or bread dumplings and apple and red cabbage.