In a small bowl, stir together all the rub ingredients Set aside.

Line two large, rimmed baking sheets with tin foil. Once the membranes are pulled off the bottoms of the rib racks, place the meat on the baking sheets. Then rub the spice mix all over the ribs, patting it all into the crevices of the meat. Cover the meat with foil and put in the refrigerator overnight.

Preheat the oven to 275℉ and remove the baking trays from the refrigerator while the oven heats up. Pour off any extra liquid that accumulated on the baking sheets overnight. Bake the ribs (still covered with foil) for 4 hours. The meat should be tender, but not falling off the bone. Remove from the oven and pour off any excess liquid.

While the ribs are cooking, make the sauce. In a saucepan over medium heat, melt the butter and sauté the onion for 10 minutes. Then stir in the garlic and thyme and sauté for another 2 minutes. Slowly stir in the ketchup, vinegar, beef broth, hot sauce (if using and you like things spicier), bourbon, Worcestershire sauce, and molasses. Slowly bring the mixture to a boil, stirring constantly. Then simmer, stirring intermittently, for 30 minutes or until the sauce thickens.

Preheat the broiler and place a rack in the top of the oven, about 12" from the broiler. Brush the sauce all over the ribs and then broil for 10 minutes, stopping to brush more sauce as the meat broils. It's done with the meat is browned and bubbly.

Remove from the oven and allow to rest for 10 minutes. Serve immediately and you can use extra barbecue sauce on the side.