How to Make It
Stir together sugar, paprika, onion powder, garlic powder, cayenne, celery salt, and thyme in a medium bowl. Transfer 3 tablespoons of the spice mixture to an airtight container; whisk in maple syrup and bourbon. Attach lid, and chill until ready to use. Stir salt into remaining dry spice mixture.
Line a large rimmed baking sheet with 2 sheets of plastic wrap, slightly overlapping plastic sheets in center, and allowing extra to hang over all sides. Spread half of dry spice mixture on plastic wrap in an even layer slightly larger than size of salmon. Place salmon, skin side up, on spice mixture. Spread remaining half of dry spice mixture in an even layer on skin of salmon. Wrap plastic wrap tightly around salmon. Place another baking sheet on top of wrapped salmon, and weight it down with a few unopened cans; chill 12 hours.
Unwrap salmon, and discard plastic wrap. Rinse off spice mixture, and pat salmon dry with paper towels. Place salmon, skin side down, on a wire rack set inside a rimmed baking sheet. Chill, uncovered, until surface of salmon forms a thin, dry skin, about 12 hours.
Fill a pellet container to an electric pellet grill with hardwood pellets according to manufacturer’s instructions. Set temperature to 180°F, close lid, and preheat pellet grill 10 to 15 minutes. Place salmon on oiled grill grate, close lid, and grill, brushing salmon with bourbon mixture every 45 minutes, until a meat thermometer inserted in thickest portion registers 145°F, 3 to 4 hours. Remove salmon from pellet grill, and place in refrigerator, uncovered, until chilled, about 2 hours.