In a large skillet, cook onion in butter over medium heat for 15-20 minutes or until onion is golden brown, stirring frequently. Stir in wine and garlic. Bring to a boil. Reduce heat; simmer, uncovered, for 3-4 minutes or until liquid has evaporated., Meanwhile, combine the rosemary, salt and pepper; rub over steaks. Broil 4 in. from the heat for 7-9 minutes on each side or until meat reaches desired doneness (for medium-rare, a thermometer should read 135°; medium, 140°; medium-well, 145°). Serve with caramelized onions.