Preheat oven to 275°F (135°C).
Remove membrane from back of ribs.
Mix all dry rub ingredients.
Pat ribs dry. Rub spice mixture all over both sides.
Wrap each rack tightly in aluminum foil.
Place on baking sheet bone-side down.
Bake for 2½ hours until very tender.
Remove from oven. Carefully open foil packets.
Brush both sides generously with BBQ sauce.
Turn oven to broil. Place rack 6 inches from heat.
Broil 3 to 5 minutes until sauce caramelizes.
Brush with more sauce if desired.
Rest 5 minutes. Cut into individual ribs. Serve hot.