Heat oven to 425°F. Rub beef with oil; sprinkle with pepper. Place beef on rack in shallow roasting pan, or place diagonally in 15x10x1-inch pan. Insert ovenproof meat thermometer so tip is in center of thickest part of beef.
Bake uncovered 30 to 45 minutes or until thermometer reads 135°F. Cover beef loosely with tent of foil and let stand 15 to 20 minutes until thermometer reads 145°F (medium-rare doneness). (Temperature will continue to rise about 10°F and beef will be easier to carve.)
Meanwhile, in 12-inch nonstick skillet, melt butter over medium heat. Cook onion, garlic and mushrooms in butter 8 to 10 minutes, stirring occasionally, until mushrooms are completely tender and beginning to brown. Stir in sherry. In small bowl, mix cornstarch and water; stir cornstarch mixture into mushroom mixture. Stir in thyme, pepper and beef consommé; cook and stir about 2 minutes or until slightly thickened and bubbly. Stir in mustard and tomato paste until well blended. Heat just until hot. Spoon sauce over sliced beef.