Preheat the 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 cooked onions, carrots, parsley and tomatoes with their liquid over brisket.

In a small bowl, mix beef broth and sugar until dissolved then pour around brisket.

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 cutting board and rest until cool enough to handle.

Trim off and discard all visible fat then slice diagonally against the grain and transfer brisket 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.