1Heat oven to 450°F. Cut beef lengthwise in half, cutting almost but not completely through; open flat. Pound to 3/4-inch thickness.
2In 12-inch skillet, cook onion in butter over medium-high heat 3 minutes or until tender. Add garlic; cook and stir 30 seconds. Add mushrooms, thyme, rosemary and 1/2 teaspoon of the salt. Cook 5 minutes or until mushrooms are tender. Stir in vinegar; cook 2 minutes or until liquid has evaporated. Cool. Spoon mushroom mixture over beef to within 1/2 inch of edges. Roll up beef, starting with long side, and tie with kitchen string at 2-inch intervals. Rub with pepper and remaining 1/2 teaspoon salt. Place seam side down on rack in roasting pan. Insert ovenproof meat thermometer so tip is in thickest part of beef.
3Bake uncovered 30 minutes or until thermometer reads at least 140°F. Cover loosely with foil; let stand 15 minutes or until thermometer reads 145°F. Garnish platter with fresh herb sprigs.