Shred the onion and cabbage and put in a saucepan with a little hot fat. Mix well and add the meat, cut in cubes, the chopped tomatoes, and the seasoning of paprika and salt. Simmer gently for 30 minutes, but without allowing to brown. Then add the hot water gradually, cover, and simmer for 1½ hours, till the meat and cabbage are quite tender. Half an hour before serving, dilute the flour with a little of the sour cream and a few tablespoons of the hot stock, work into a smooth paste, and stir it into the soup. Finally stir in the remainder of the sour cream.