Heat oven to 350. Heat a heavy oven proof pot over medium high heat. When hot; add oil and heat oil until hot. Add brisket and cook until browned turning once, about 5 minutes. Remove from pot to plate and sprinkle both sides with thyme, salt and pepper.
Melt butter in the pot over medium heat and add onions. Stir to coat with butter and then cover and cook for 5 minutes. Uncover and turning heat to medium high and cook onions until they start to brown. Add garlic and stir for 30 seconds, then add broth, wine and worcestershire sauce.
Return brisket to pot; spooning the onions to the top of the roast. Around the roast place the carrots and potatoes. Cover and bake for 1 hour or until vegetables are tender and meat is tender.
Remove brisket and let is rest for 10-15 minutes on a cutting board covered loosely foil.
Thinly slice the brisket and serve with the vegetables still in the pot. Spoon some of the juices over the roast.