Place ribs in ungreased 13x9-inch pan; cover with foil. Bake at 350°F. for 1 hour.
Meanwhile, in small saucepan, combine apple butter, barbecue sauce and onion; mix well. Bring to a boil, stirring occasionally. Reduce heat; cover and simmer 15 to 20 minutes.
Heat grill. When ready to grill, brush 1 side of ribs with apple butter mixture. Place ribs, apple mixture side down, on gas grill over medium heat or on charcoal grill 4 to 6 inches from medium coals. Brush top of ribs with mixture; cook 10 to 15 minutes or until pork is browned, turning and brushing occasionally with apple butter mixture.
Bring any remaining apple butter mixture to a boil. Serve mixture with ribs.