How to Make It
Preheat the oven to 325°. Spread the onions in a roasting pan that will hold the meat snugly.
On a work surface, mince the garlic with 1 teaspoon of kosher salt to make a paste. Transfer the paste to a small bowl and stir in the oil and 1/2 teaspoon of pepper. Rub this paste all over the brisket. Set the brisket, fat side up, on the onions. Pour the tomato juice and water around the meat and add the bay leaves.
Cover the pan tightly with foil, transfer to the oven and braise the meat for 3 to 4 hours, or until very tender. Uncover the pan and bake for 30 minutes longer, or until the top is lightly browned and the cooking liquid has thickened slightly.
Transfer the meat to a carving board and discard the bay leaves. Strain the cooking liquid, reserving the onions. Skim the fat from the surface of the cooking liquid and discard. In a food processor, puree the cooking liquid with half of the onions. Transfer the sauce to a medium saucepan, season with kosher salt and pepper and keep warm over low heat.
In a saucepan, reheat the remaining onions with some of the sauce and season with kosher salt and pepper. Carve the meat across the grain into thin slices and transfer to a large serving dish. Pour the hot sauce over the meat and serve at once, passing the onions separately.