Combine the brown sugar, granulated sugar, chili powder, garlic powder, onion powder, paprika, 2 teaspoons salt and a generous amount of freshly ground black pepper in a small bowl (30 grinds).
Place the ribs on a piece of foil large enough to fold over and seal, then place on a baking sheet. Sprinkle the dry rub all over the top of the meaty side of the ribs. Wrap the foil around the ribs and seal tightly so that no juices can escape during baking. Bake until the meat is tender and can easily be pulled away from the bones with a fork, about 2 hours.
Heat the BBQ sauce in a small pan over medium heat until warm. Remove the ribs from the oven and open the foil pack. Remove the ribs from the foil and pour any juices that have accumulated into the BBQ sauce and mix to combine. Continue to simmer the sauce until thickened, about 7 minutes.
Heat a grill or grill pan for cooking at medium-high heat
Slice the ribs into 1-bone pieces. Brush all over with the BBQ sauce. Place the ribs on the grill and cook until grill marks appear, a few minutes on each side.
Flip and grill another minute or so, just until the rounded side is softened. Remove from the grill with tongs.