Set the brisket on a large sheet of plastic wrap. In a medium bowl combine the dark brown sugar, chili power, paprika, salt, garlic powder, onion powder, black pepper, cayenne, dry mustard, and cumin thoroughly. Rub the mixture onto the brisket and wrap tightly in the plastic wrap. Place on a baking sheet and let marinate refrigerated at least 6 hours or overnight. Remove the meat from the refrigerator and let come to room temperature.
Soak mesquite wood chips in a large bowl of water for 1 to 2 hours. Remove, drain and set aside.
Remove the meat from the refrigerator and let come to room temperature.
Prepare a smoker with charcoal and the wood chips according to the manufacturer's instructions to 180 to 200 degrees F. Place the water pan in the smoker and add water to the fill line, about 2/3 full. Place the unwrapped brisket on the lower rack off the direct heat, close the lid, and cook, regularly stoking the fire and adding additional chips, until an instant-read thermometer registers an internal temperature of 140 to 145 degrees F., about 4 to 5 hours. Remove the meat from the grill and let rest for 20 minutes before carving the meat against the grain.
(Alternately, prepare a stove-top smoker according to the manufacturer's instructions. Place the unwrapped brisket on the rack over low heat. Close the lid and smoke for 1 hour. Preheat the oven to 275 degrees F. Remove the meat from the smoker and wrap in a large sheet of heavy aluminum foil. Place on a baking sheet and roast until tender and an instant-read thermometer registers an internal temperature of 140 to 145 degrees F., about 2 to 3 hours. Remove the meat from the oven and let rest for 20 minutes before carving the meat against the grain.) Serve with Barbecue Sauce on the side for dipping.
BBQ Sauce - In a large pot, heat the oil over medium-high heat. Add the onions and cook, stirring, for 4 minutes. Add the garlic and cook, stirring, for 1 minute. Add the ketchup, brown sugar, cane syrup, vinegar, mustard, Worcestershire, hot sauce, Southwest Texas Seasoning, and red pepper flakes and bring to a boil. Lower the heat and simmer, stirring occasionally, until thickened and the flavors marry, 15 to 20 minutes. Remove from the heat and let cool slightly before serving. Yield: about 4 cups
Southwest Texas Seasoning:
Combine all ingredients thoroughly and store in an airtight jar or container. Yield: about 2/3 cup
Note: EVEN BETTER when brisket is marinated overnight in a large ziplock freezer bag-in the fridge!