Note: I buy coriander seeds and whole peppercorns from the local GFS store and grind them using an old blade-style coffee grinder. Make sure you keep the grind a little coarse. You can also use a mortar and pestle.
Rinse and dry the corned beef.
Whisk together the mustard, brown sugar, coriander and allspice. 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.