In a small bowl, beat the first 5 ingredients. Cut a pocket horizontally in steak; fill with butter mixture., Grill steak, covered, over medium heat or broil 4 in. from heat until meat reaches desired doneness (for medium-rare, a thermometer should read 135°; medium, 140°; medium-well, 145°), 5-7 minutes on each side. Let stand 5 minutes before serving. To serve, slice across the grain.