Heat oven to 350°F. In 12-inch nonstick skillet, heat oil over medium-high heat. Add beef roast; cook until browned on both sides. Place roast in center of ungreased shallow roasting pan or 13x9-inch (3-quart) glass baking dish. Sprinkle with salt and pepper.
In same skillet, cook onion over medium-high heat 4 to 6 minutes, stirring occasionally, until tender. Stir in broth, molasses and thyme. Heat to boiling. Boil 5 minutes, stirring occasionally. Pour broth mixture over roast. Cover tightly with foil.
Bake 1 hour. Place sweet potatoes and parsnips around roast; bake 1 to 1 1/4 hours longer or until roast and vegetables are fork-tender.
Remove roast and vegetables from pan, reserving juices. Pour juices into 2-quart saucepan. In small bowl, mix flour and water until smooth. Place saucepan with drippings over medium heat; gradually stir in flour mixture, cooking and stirring, until mixture comes to a full boil. Boil 1 minute, stirring constantly, until thickened. Cut roast into slices; serve with vegetables and gravy.