an offset smoker, optional; a food-safe spray bottle; peach butcher paper; an instant-read thermometer
Set up your grill for indirect heat by building the coals on one side only. Allow the temperature to reach 225 to 250 degrees F. Alternatively, set up your offset smoker. Build a fire with apple and cherry wood in the firebox and allow the temperature to reach 225 to 250 degrees F and the smoke to begin to run clear.
Clean the brisket by trimming the fat cap, creating a fatty and lean side. Trim the fat on the point down to about 1/2 inch. Trim the fat on top of the flat end down to about 1/4 inch. Flip the brisket over and remove any silver skin and sinew from the meat. You will lose around 2 pounds from trimming.
Place the fat you have trimmed into a small pan and place on the smoker or grill to render. You will use it later to brush the brisket before wrapping.
To make the pastrami spice, add the coriander seeds, black pepper, salt, mustard seeds, chili flakes and sumac to a small bowl and mix to combine. In a spray bottle, combine the apple cider and Worcestershire sauce.
Coat the entire brisket with the mustard, then liberally season on all sides with the pastrami spice. Spray it with the apple cider mixture.
Place the brisket on the indirect side of the grill with the fat side facing down. If using the smoker, place the brisket with the fattiest part of the brisket pointed towards the fire. Place a thermometer in the fattest part of the brisket, close the lid and cook, misting the brisket every 30 minutes, until it reaches an internal temperature of 165 degrees F, about 6 hours.
Brush the brisket with the rendered fat and wrap it in peach butcher paper. Place back onto the indirect heat on the grill or smoker and continue to cook until an internal temperature of 205 degrees is reached, about 3 more hours.
Remove from the grill and let rest for at least 1 hour before separating the flat (lean brisket) from the point (fatty brisket). Slice against the grain and serve.