In a non-aluminum bowl or pan, combine the brisket with the marinade ingredients. Refrigerate for 24 hours, turning once.

Preheat the oven to 400°.

Remove the brisket from the marinade and dry with paper towels. Reserve the marinade. Rub in the salt and pepper and spices. Lightly dredge with flour. In a large heavy skillet, brown the brisket, fat side down, over moderate heat. Turn and brown all over.

Remove the meat to a large non-aluminum ovenproof casserole or Dutch oven. Strain the marinade, discarding the solids. Pour the liquid into the skillet and deglaze over moderately high heat, scraping up the brown bits that cling to the bottom of the skillet. Simmer for 5 minutes. Pour the liquid over the meat and cover with onions. Cover the casserole and bake for 30 minutes.

Remove the cover and continue cooking for 1 hour. Cover again and cook for 1 to 1 1/2 hours more, until the meat is fork-tender. Let the brisket rest for 10 to 15 minutes. Serve with the onions and pan juices.