Whisk together the mustard, brown sugar, coriander and allspice. You want the mixture to be slightly wet so that it adheres to the meat. If it does not, add a bit more mustard and mix.
Rub the mixture all over the brisket, then cover completely with the ground pepper. Place in a large resealable bag or wrap tightly in foil and keep in the fridge overnight.
The next day, fire up your smoker for 225-250 F. Place a chunk or two of light fruit wood in the smoker (I used cherry). Cook the brisket for at least 8 hours or until the internal temperature reaches 195 - 205 F.
Remove, wrap in foil, and let rest for 30 minutes.
Thinly slice the brisket against the grain using a meat slicer or sharp knife. Serve.
Notes
I usually buy reduced sodium corned beef to make pastrami. If you have concerns over the amount of sodium, soak your brisket in cold water for 2 hours, replacing the water every 30 minutes.