There are different versions of this recipe from all over the Balkans. You may be able to get sour cabbage from an Eastern European market; if not, you can boil the cabbage heads until soft enough to work with (the dish will taste slightly different - maybe add some vinegar to the broth). It is a very filling dish! Don't worry about leftovers, they taste just fine reheated (use the stove, not the microwave)!