Mix first 5 ingredients and generously rub into ribs. Refrigerate, uncovered, for 4 to 24 hours.
Preheat oven to 300 degrees. Separately wrap each rack in heavy-duty aluminum foil, put packets in a shallow pan, and cook for 2 hours. Remove from oven, open foil, and let cool for about 45 minutes. Reseal foil packets. At this stage, you can refrigerate overnight and reheat the next day.
Prepare a balsamic reduction by bringing the vinegar to a boil over medium-high heat. Immediately reduce heat and simmer 8 to 10 minutes or until it’s thick enough to coat the back of a spoon. Set aside. When ready to serve ribs, set oven to broil. Remove from foil and slice into 1- or 2-bone pieces. Put in a roasting pan along with 2 to 3 tablespoons of water, place in upper third of oven, and reheat until nicely caramelized, 7 to 10 minutes (be careful not to burn). Brush with balsamic reduction and serve on Moroccan Slaw.