In a large stockpot, place both racks of ribs; add enough water to cover meat. Add marinade, bay leaves and onion. Bring mixture to a boil over high heat. (This will create foam on top.)
Reduce to medium-low heat; simmer 45 minutes or until ribs are just tender. Remove ribs from cooking liquid; drain on rimmed baking sheet. Heat grill to medium heat, about 350 degrees.
In a small mixing bowl, stir the barbecue sauce and brown sugar. Brush over both sides of ribs. Place ribs on grill, bone side down and close lid. Grill for 7 minutes; turn and grill 7 minutes more.