How to Make It
Heat the olive oil in a large skillet. Add the minced onions and the Thai chiles and season with salt. Cook over low heat, stirring occasionally, until the onions are very soft, about 25 minutes. Increase the heat to moderately low and cook, stirring, until the onions are deeply browned, about 10 minutes longer.
Preheat the oven to 325°. Spread the carrots, celery and coarsely chopped onions in an even layer in a roasting pan and season them with salt and pepper. Season the brisket with salt and pepper and set it on top of the vegetables, fat side up. Spread the onion-and-chile jam in an even layer over the top of the brisket and pour the hot stock into the pan around the meat. Cover the roasting pan and braise the brisket for about 4 1/2 hours, or until it is very tender, basting every 30 minutes.
Let the brisket rest in the pan juices for 30 minutes, then transfer it to a carving board. Strain the pan juices into a saucepan, pressing on the vegetables, then skim off the fat. Add the soy sauce, season with pepper and bring to a simmer. Thinly slice the brisket across the grain and serve with the pan juices.