- 2 cups hot water
- 1 cup balsamic vinegar
- 1/2 cup packed dark brown sugar
Marinate and roast ribs:
Mince and mash garlic to a paste with 1 teaspoon salt. Stir together with rosemary, brown sugar, vinegar, cayenne, 1 tablespoon salt, and 1 teaspoon pepper. Rub evenly all over ribs and transfer to roasting pans. Marinate, chilled, 8 to 24 hours.
Preheat oven to 425°F with racks in upper and lower thirds.
Pour 1/2 cup water into each roasting pan and tightly cover pans with foil. Roast ribs, switching position of pans halfway through, until meat is very tender, about 1 3/4 hours. Remove pans from oven and transfer ribs to a platter.
Make glaze and grill ribs:
Add 1 cup hot water to each roasting pan and scrape up brown bits. Skim off and discard fat, then transfer liquid to a 10-inch skillet. Add vinegar and brown sugar and bring to a boil, stirring occasionally. Boil until reduced to about 1 cup, about 15 minutes.
Prepare grill for direct-heat cooking over medium-hot charcoal (medium heat for gas); see Grilling Procedure .
Brush some of glaze onto both sides of racks of ribs. Grill, turning occasionally, until ribs are hot and grill marks appear, about 6 minutes.
Brush ribs with more glaze and serve remaining glaze on the side.