Remove papery outer skin from garlic bulb (do not peel or separate cloves). Cut top off of garlic bulb; brush with 1/2 teaspoon oil. Wrap bulb in heavy-duty foil. Bake at 425° for 30-35 minutes or until softened. Cool for 10-15 minutes. Squeeze softened garlic into a small bowl; mash and set aside.
Sprinkle steak with pepper and salt. In a large nonstick skillet coated with cooking spray, cook steak over medium-high heat in remaining oil for 3-4 minutes on each side or until browned.
Reduce heat to medium; add 1 tablespoon butter. Cook steak 4-8 minutes longer on each side or until meat reaches desired doneness (for medium-rare, a thermometer should read 145°; medium, 160°; well-done, 170°). Remove and keep warm.
Gradually add broth and wine to the pan, stirring to loosen browned bits. Bring to a boil. Stir in mashed garlic. Reduce heat; simmer, uncovered, until liquid is reduced by half.
Strain sauce and return to pan; stir in remaining butter until melted. Thinly slice steak across the grain. Sprinkle with onions; serve with sauce. Yield: 6 servings (3/4 cup sauce).