Combine the salt, thyme and pepper; rub over roast. Place fat side up on a rack in a shallow roasting pan. Bake, uncovered, at 350 degrees for 3 hours or until meat reaches desired doneness (for medium-rare, a meat thermometer should read 145 degrees; medium, 160 degrees; well-done, 170 degrees). Transfer to a warm serving platter. Let stand for 20 minutes.

Meanwhile, for gravy, pour pan drippings and loosened browned bits into a 4-cup measuring cup. Skim fat, reserving 1/4 cup; set drippings aside. In a skillet, saute the mushrooms and onion in reserved fat until tender. Add tomato paste; cook and stir until combined. Remove from heat.

Add enough beef broth to reserved drippings to measure 3 1/2 cups. In a large saucepan, combine the flour, wine, lemon juice and broth mixture until smooth. Stir in mushroom mixture. Bring to a boil; cook and stir for 2 minutes or until thickened. Season with salt and pepper. Slice roast and serve with gravy.

Makes 14 to 16 servings.