How to Make It
Boil the water in a large pot. Add the beef and return to a boil; skim. Add the onion, tomato paste, thyme and peppercorns. Season with salt and simmer over low heat for 3 hours, skimming.
Cook the cabbage in boiling salted water for 5 minutes; drain. Tie the leeks and celery into a bundle with string. Add the cabbage, leek and celery bundle, carrots and turnips to the beef and simmer over moderately low heat for 30 minutes.
Cook the potatoes in boiling salted water until tender, about 20 minutes; drain. Add the potatoes to the beef and cook until all the vegetables and the meat are tender, about 20 minutes longer.
Skim the broth. Remove the leek bundle from the pot and discard the string. Spoon the meat and vegetables into soup plates, ladle a little of the broth over them and serve. Pass the mustard, cornichons, salt and pepper separately.