i used this recipe from feastie.com, with one kind of significant change. the writer had noted that by adding the balsamic vinegar it caused her jam not to set quite as well, but that the enhanced flavor was well worth it. so instead of adding the 1/4 cup of balsamic vinegar that the recipe called for, i first used 1/2 of balsamic and created a reduction with it (ie. in a pot or pan, heat it to boiling and then simmer it for about 5-10 minutes, stirring occasionally. it will thicken up, especially once it cools, and you'll end up with less than 1/4 cup but a lot of flavor). mine set beautifully.
here's how it all went down:
i was well prepared...
otherwise, get your jam on and enjoy!