Combine thyme, oregano, salt and pepper; rub over both sides of brisket.
In flameproof roasting pan heat oil over medium-high heat; add brisket. Cook, turning once, until browned, 3-4 minutes per side. Remove from heat.
Add onions, garlic and bay leaves to pan around brisket; pour in wine. Cover; roast 1 hour, 30 minutes. Turn brisket over; roast, covered, until very tender, 1 hour, 30 minutes.
Transfer brisket and half onions to serving platter; cover with foil. Transfer drippings and remaining onions to blender; pulse until smooth. Slice beef against the grain of the meat and serve with sauce.