Pat the corned beef brisket dry with a paper towel. Once dry, rub it with 2 tbsp of stone ground mustard.
Evenly apply the dry spice rub to the brisket, using all of the spice rub.
Preheat your smoker to 230F, and fill up your smoker’s water tray. If using a smoke tube, start it now.
With the smoker ready, place the corned beef directly on the smoker rack. If your corned beef has a fat layer, orient the corned beef so the fat is on top.
Start smoking your meat, you’ll probably experience a stall between 140F and 165F. Once you get past the stall, around 170F, you can wrap the corned beef in foil or butcher paper. Increase the smoker’s temperature to around 270F and continue smoking. This will help finish the cook in a reasonable time.
When the pastrami reaches 200F, pull the pastrami from the smoker and stow in an empty cooler for 30-60 minutes to let it rest.
Slice the pastrami to your desired thickness and serve!