Soak the porcini in 1 cup water for 2 hours. Drain them, pat dry with paper towels, chop fine, and set aside. Discard the liquid or save for another use.
To make the stock, in a large soup pot, bring the meat, bones, and water to a boil over high heat, periodically skimming off the foam as it rises to the top. Add the remaining stock ingredients, and reduce the heat to low. Simmer, covered, until the meat is tender; about two hours.
Meanwhile, melt half the butter in a deep skillet over medium heat> Add the cabbage and sauerkraut and saute for 10 minutes, tossing and stirring regularly. Add one cup hot stock (it doesn't have to be fully cooked) and the tomato paste. Cover and simmer over low heat for 35 to 40 minutes.
Melt the remaining butter in another large skillet and saute the carrot, onions, celery, turnip, and mushrooms until soft and lightly browned; about 15 minutes. When the stock is ready, strain it into a clean pot. Reserve the meat and discard the other solids. Add the sauerkraut and cabbage, the vegetable mixture, and tomatoes to the stock. Season with salt and pepper, stir, and cook, covered, over medium-low heat for 20 minutes.
Cut the meat into bite-size pieces and add it to the soup, along with the minced garlic. Simmer for another five minutes. Let stand for at least 15 minutes, and preferably a day and a night, before serving; refrigerate, covered, and reheat slowly if serving the next day. Serve garnished with fresh dill and sour cream, if desired.
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