Method:
Preheat oven to 350°F. Sprinkle brisket all over with salt and pepper then arrange fat side up in a heavy roasting pan.
Heat oil in a large skillet over medium high heat. Add onions and cook, stirring occasionally, until just golden brown. Scatter onions, carrots, parsley and tomatoes with their liquid over brisket. In a small bowl, mix beef broth and sugar until dissolved then pour around the brisket and cover the pan tightly with foil.
Roast, turning brisket and stirring vegetables once or twice during cooking, until meat is very tender, about 3 hours. Transfer brisket to a large platter and set aside until cool enough to handle. Trim off and discard all visible fat then slice diagonally against the grain and return meat to a platter; tent with foil to keep warm. Simmer pan juices until reduced slightly to make a sauce, if desired, then spoon over beef and serve.