Preheat the oven to 300 degrees F.
Pat the brisket dry and sprinkle with the salt and pepper. Heat 1 tablespoon of the oil over medium-high heat in a Dutch oven or braising pot. Sear the brisket until it is browned, 4 to 5 minutes per side. Transfer the brisket to a plate.
Add the remaining 1 tablespoon oil to the pot and cook the onion, stirring a few times, until softened, 3 to 5 minutes. Add the garlic and cook, stirring, for 1 minute. Add the tomato sauce, broth, brown sugar, 1/3 cup of the vinegar, the raisins, peppercorns, and allspice and stir to combine well. Bring mixture to a boil, return brisket and any accumulated juices to the pot, spoon some of the tomato-vinegar mixture over the brisket, cover tightly, and transfer to the oven. Cook until the brisket is fork tender, 2 1/2 to 3 hours.
Remove the brisket from the oven, transfer the meat to a cutting board, and let rest for 10 to 20 minutes or, if serving later, cover and refrigerate the meat and sauce for several hours or overnight. When you are ready to serve, cut the meat against the grain into 1/4- inch thick slices. Stir the remaining 1 tablespoon vinegar into the warm sauce. Return the sliced brisket to the sauce until heated through, then serve.
Yield: 10 servings, serving size: 4-ounces brisket plus 3 tablespoons of sauce