In a large pot mix together brown sugar, curing salt, pickling spice and whiskey. Over a medium- high heat bring to a boil, then let cool to room temperature.
Clean and trim your brisket. Once your brine has come to room temperature add in your brisket, cover and refrigerate for 3 days. Turn your brisket 180 degrees twice per day. (morning and night). You may need to weigh down your brisket to keep it submerged, the best way to do this is with a bag of ice held down with a heavy plate or pan.
After 3 days drain your brisket and discard your brine. Soak the brisket in fresh cold water for around 20 - 30 minutes, then drain again.
Preheat your grill or smoker to 250°F following your manufacturer's instructions for indirect grilling.
When you have reached temperature, place your brisket in fat side down. Smoke the brisket for about 4.5 hours and check the internal temperature. You are looking for an internal temperature of 180°F, this should take anywhere from 4.5 - 5.5 hours.
Once the brisket has reached temperature, wrap in butcher paper and continue to smoke for a further hour. Or until you have reached an internal temperature of 195°F.
When you are reached an internal temperature of 195°F keep your brisket in its butcher paper and rest for 1 hour (or at least 40 minutes if you really can't wait). Once well rested slice against the grain and serve immediately.