Trim the excess fat off of the brisket, leaving a 1/4 to 1/2-inch layer of fat cap.
Apply a generous amount of salt and pepper and the sugar-free rub to all sides of the brisket, massaging the seasonings into the meat until it's evenly coated.
Inject the beef broth throughout the brisket using the meat injector.
Cover with foil and rest the brisket in the fridge for 2-24 hours to allow the seasoning and broth to seep into the meat.
Take the brisket out of the fridge up to two hours before you're ready to place it on the smoker to allow it to get to room temperature.
Preheat the grill to 225°F. Place a foil pan with water under the bottom grate to keep the smoker humidity level high.
Place the prepped brisket directly onto the smoker, fat side up.
Smoke the brisket for 1.5 hours per pound of brisket, until it reaches 160°F in multiple parts of the meat.
Remove the brisket from the smoker, put in on foil in a large pan. Fold the sides of the foil up to create a bowl.
Mix the beef tallow and melted butter together, and pour over the brisket, making sure the liquid stays in the foil. Fold the foil over the meat, completely covering the brisket.
Place the covered brisket back on the smoker on the pan and all it to reach an internal temperature of 201°F.
Remove the brisket from the smoker and allow it to rest for about two hours to allow the juices to redistribute evenly through the meat.
Finally, slice the brisket against the grain and serve.