From her cookbook From Julia Child's Kitchen. The meat can rest after cooking, from 1 to 24 hours or more. Julia notes that brisket is never tender like steak, but should be pleasantly chewable and have a strong beefy flavor.
In a small bowl, mash the salt and thyme into the puréed garlic with the flat side of a large kitchen knife.
Beat the oil and pepper into the garlic mixture and spread this mixture over both sides of the brisket.
Toss the vegetables in a large bowl with a little salt and thyme.
Spread half of the vegetable mixture in the bottom of a roasting pan.
Place beef, fat side up, on top of the vegetables.
Cover with the remaining vegetables.
Cover the pan tightly with foil.
(This dish may be prepared to this point in advance and refrigerated.).
When ready to cook, cook--basting with pan juices every 1/2 hour--in a 300° oven 3-4 hours until a fork goes into the meat easily; by the end of cooking, the meat will have shrunk.
**** If you are not serving the meat until the next day, transfer the meat with its vegetables to a smaller pot; degrease the juices and pour them over the brisket and chill, uncovered, until cooled; then cover and keep in the refrigerator up to 2 days. To reheat, put this dish in a 350° oven for 20 minutes, basting 2-3 times with its juices. ****.
Remove the beef with its vegetable topping to a cutting board.
Pour the juices into a saucepan, degrease, and rapidly boil down almost to a syrup.
If you wish, you can thicken the juice into a sauce with 1-1/2 Tbs cornstarch blended with 2 Tbs of either wine or stock.
Carve the meat across the grain into thin slanting slices.
Accompany each serving of meat with 1-2 spoonfuls sauce and vegetables.