
Preheat oven to 500 degrees F.
Using a paring knife, cut small slits in the brisket. Stuff brisket all over with garlic, if using. Rub sugar on both sides of the brisket. Place brisket in a baking pan or casserole and bake until browned on top, about 25 Minutes. Remove from oven, turn brisket and return to oven until browned on both sides.
Reduce oven temperature to 350 degrees F. Add enough chicken stock to the pan to come up 1 inch on sides, cover with foil and bake one hour.
While brisket is cooking, heat a large skillet over medium high heat and sauté onions in oil, stirring occasionally, until caramelized and most liquid has evaporated, about 20 Minutes. Set aside.
Remove brisket from oven after one hour and add caramelized onions. Season meat generously with salt and pepper. Cover and continue to bake until very tender but not falling apart, another hour. Remove from oven and cool.
Place brisket on a carving board and slice.
Brisket is better if made a day in advance so return it to the pan, refrigerate and reheat before serving.
