Preheat the oven to 350 degrees F (175 degrees C). Trim any excess fat from the ribs and remove the thin membrane from the back of the ribs using a paper towel to grip it.

In a small bowl, combine garlic powder, onion powder, paprika, salt, black pepper, and 2 tablespoons of brown sugar. Rub this mixture generously over both sides of the ribs.

Place the ribs on a baking sheet lined with aluminum foil, meat side up. Cover tightly with another sheet of foil. Bake in the preheated oven for 2 hours or until the meat is tender but not falling off the bone.

While the ribs are baking, combine the remaining brown sugar, vinegar, ketchup, Worcestershire sauce, rum (if using), liquid smoke (if using), cayenne pepper, and butter in a saucepan over medium heat. Bring to a simmer, stirring occasionally, and cook for about 15 minutes until slightly thickened. Remove from heat and set aside.

About 15 minutes before the ribs are done baking, preheat your grill to medium heat (about 350-400 degrees F).

Remove the ribs from the oven and carefully transfer them to the preheated grill, meat side down. Grill for 5 minutes.

Flip the ribs over, brush generously with the BBQ sauce, and grill for another 5 minutes.

Continue to flip and baste the ribs every 5 minutes for about 20-30 minutes total, or until the sauce has formed a sticky glaze and the ribs have a nice char in spots.

Remove the ribs from the grill and let them rest for 10 minutes. Cut between the bones and serve with any remaining BBQ sauce on the side.