Cook onions and garlic in oil until lightly colored. Remove from heat and stir in paprika. Pour in 1/2 cup of stock or water, bring to a boil, then add the pork cubes. Spread sauerkraut over the meat, sprinkle with caraway seeds. In a small bowl combine tomato puree, rest of the stock or water and pour over the sauerkraut. Bring to a boil. Reduce heat, cover and simmer for 1 hour. Add little stock or water if needed. When the pork is tender, combine sour cream and heavy cream; beat in flour. Stir the mixture into the casserole. Simmer for 10 minutes longer. Taste for seasoning. Serve in deep platter, accompanied by a bowl of sour cream.