Coat the shanks lightly in flour and fry in a large pot or dutch oven till browned on all sides. Drain off excess fat and oil. Add salt and pepper, water and onion to the pot. Cook, covered over low heat until tender, about 1 1/2 hours - adding more water if necessary and turning the shanks occasionally.
Finally, stir in the tinned soup and sour cream. Cook, covered, for about 10 minutes more, then serve.