Begin brining the brisket 1 or 2 days before smoking. Select a stockpot or other vessel large enough to hold the brisket and about 4 quarts of water.Pour in 2 quarts of water. Add the salt, garlic, and bay leaves. Stir to dissolve the salt. Rinse the brisket under running cold water and place in the brine. Add water just to cover. Cover and refrigerate for 24 - 36 hours, turning the meat once or twice.

The day before smoking the meat, make the sauce: In a large, heavy non-aluminum pan over medium-high heat, warm the corn oil. Add onions and salt and sauté, stirring often, for 3 minutes. Add the chile powder, 2 teaspoons black pepper, celery seed, allspice, mace, and cayenne pepper and stir and toss to coat the onions. Cook until fragrant, about 1 minute. Pour in the vinegar and stir to scrape up any browned bits on the pan bottom. Stir in the mustard, brown sugar, and molasses. When the mixture comes to a boil, add the tomatoes and return to a boil.

Reduce the heat to very low, cover partially, and cook, stirring occasionally and mashing the tomatoes, for 3-3½ hours. Using a blender and working in batches, purée the sauce, adding water as needed to reach the desired consistency. It should be thick but pourable. Adjust the seasoning with sugar, salt, and black pepper. Cover and refrigerate until ready to use.

On the morning you will begin smoking, make the rub: In a spice mill or clean coffee grinder, combine the black and white peppercorns, celery seed, caraway seed, and mustard seed and grind finely. Remove the meat from the brine and rinse thoroughly. Pat dry with paper towels and rub with the spice mixture, coating well on all sides. Set aside for 1-2 hours to come to room temperature.

Prepare a fire for indirect-heat cooking in a covered grill, building it on one side of the grill bed and starting with about 2 quarts hardwood charcoal. Light the fire, and open the vent beneath it. Place a drip pan on the other side of the grill bed. When the coals are almost all white, spread them a little but keep them to one side. Add a handful of fresh charcoal. Replace the grill rack.

Place the brisket, fat side up, on the rack over the drip pan.The fire should not be under the meat. Close the lid and open the vent on the lid so an opening is over the meat. Check the fire every 30 minutes to make sure it is still hot, adding 6 or 7 coals at a time.

The goal is to keep the temperature inside the grill around 220°F. If it is too high, the meat will be dry; if it is too low, microbial growth will occur. Continue smoking the brisket for 8-10 hours. Do not worry if the crust turns very dark.The brisket is ready when it is tender and firm but not dry when cut into at the center and an instant-read thermometer inserted into the thickest part registers at least 160°F. Remove from the grill and let rest for 15 minutes.

Gently reheat the barbecue sauce. Slice the brisket thinly against the grain and serve with the sauce and with the sandwich bread, if desired.