Preheat the oven to 325°F.

Heat the oil in a very large skillet over high heat. Place the brisket fat size down in the pan and cook until the first side is browned, 5 to 7 minutes. Season the exposed side of the brisket with ½ teaspoon salt and ¼ teaspoon pepper. (Because this is a large cut of meat, you may not be able to fit it in your skillet. The solution is to brown the brisket in the skillet in sections, letting half the brisket extend over the edges of the skillet and then turning it around to brown the other half, or to brown it in your roasting pan, set over two burners.) Turn the brisket over and brown the other side. Season the newly exposed side with another ½ teaspoon salt and ¼ teaspoon pepper. Remove from the heat.

In a large bowl, combine the onions, garlic, brown sugar, Worcestershire, mustard, vinegar, chili powder, paprika, 1 teaspoon salt, ½ teaspoon black pepper, the ketchup, and water (use some of the measured water to rinse out the ketchup bottle and pour that liquid into the bowl). Stir until well blended.

Transfer the brisket to a roasting pan or Dutch oven big enough to hold it with about an inch of space around it. Place the bay leaves on top of the meat and pour the ketchup mixture over. Cover the roasting pan (using aluminum foil if the pan doesn’t have a cover) and cook for 2 hours.

Remove the brisket from the oven and uncover. Spoon off any visible fat, if you like, and let cool briefly. (Leave the oven on.)

When the brisket is cool enough to handle, scrape off the cooking liquid clinging to it and transfer the meat to a cutting board. Cut the brisket on an angle across the grain into thin slices, less than ¼ inch thick. As you slice the meat, transfer the slices back to the roasting pan, arranging them neatly in the cooking liquid.

When all of the meat is sliced, pour any juices on the cutting board back into the roasting pan, re-cover it, and return it to the oven. Continue cooking until the meat is tender enough to cut with a fork and the cooking liquid has thickened enough to form a nice gravy, another 1 ½ to 2½ hours. Remove from the oven and remove the bay leaves.

Serve the brisket immediately, with the gravy, or let it cool. Lift the meat out of the gravy and store the meat and gravy separately in the refrigerator for up to 2 days.

To reheat the brisket if made ahead, arrange the sliced meat in a roasting pan, cover with the gravy, and heat in a 325°F oven until warm, for 30-45 minutes.