1. Begin by trimming your brisket. Remove the fat from the exterior of the point (Fatty half) and leave 1/4 inch of fat across the flat (Lean half). Remove the silver skin and the thick, stringy membrane. To help the center fat render, cut into the seam of fat which runs between the two brisket muscles, about 1 inch.
2. Spread a thin layer of yellow mustard on all sides of the brisket. This will act as a binder and help the rub stick to the meat. Additionally (And maybe more importantly) It will help to build up the bark on the brisket.
3.Liberally season all sides of the brisket, with the Grim Reaper Rub. This rub is designed to bring a lot of flavor and help to build the bark on your brisket. For a 14-16 pound brisket, you will use about 1/2-3/4 of a bottle of the rub. As you season, focus on keeping the rub layered evenly and getting consistent coverage.
4. Place brisket onto a preheated smoker at 225F and add your favorite smoking wood. Brisket is a large cut of meat, so just about any smoking wood will work. Oak and Hickory are common. Add a water pan between the meat and the heat source. Place a foil tray with your fat trim beneath the brisket to catch drippings and allow the fat to render as the brisket cooks
5. Allow the brisket to smoke directly on the grills, with the thickest part of the brisket towards the heat. After the first two hours, begin spritzing all visible sides of your brisket with the beef stock every 90 minutes.
6. Once your brisket hits about 150F, place a double layer of foil beneath the brisket and curl up the edges on all sides to form a boat shape. If the foil isn’t wide enough, you may have to stagger the foil to make it a large enough boat for your brisket. Curl up the sides to about 1 inch high.
7. Place your brisket back onto the smoker and spoon your rendered tallow onto the brisket. Continue to spritz regularly (Every 90 minutes or so) with beef stock.
8. Smoke the brisket until a thermometer inserted into the thickest part of the brisket hits 200F. Check that the probe slides into both the point and the flat easily. For a brisket this size, it will take about 15-17 hours.
9. Remove the brisket from the cooker and tent lightly in foil for 120 minutes before slicing against the grain and serving.
10. Remember, the grain of the brisket runs in different directions on the point and the flat. To help with slicing against the grain, begin by slicing the brisket width ways, separating the two muscles. Slice the flat into 1/4 inch thick slices and the point into 1/3 of inch slices.