Preheat oven to 300° and line a baking sheet with aluminum foil. If your ribs have a thin membrane over the bones on the backside, remove by carefully sliding a knife under the membrane and then peeling it away.
In a small bowl, combine brown sugar and seasonings. Rub mixture all over ribs until well coated.
Evenly distribute butter cubes over ribs, wrap tightly in foil, and place on prepared baking sheet. Bake until very tender, about 2 1/2 hours.
Switch oven to broil, unwrap ribs, and brush all over with barbecue sauce. Place back on baking sheet and broil until sauce starts to caramelize, 5 minutes.