Preheat your smoker to 250-275°F for indirect cooking. Add your preferred smoking wood — hickory or oak are ideal for beef.
Coat the chuck roast all over with a thin layer of yellow mustard. In a small bowl, mix together the kosher salt, black pepper, and garlic powder. Season the roast generously on all sides, pressing the rub in to adhere.
Place the chuck roast directly on the smoker grates, fat-side up. Close the lid and smoke unwrapped until the internal temperature reaches 165°F — approximately 4-5 hours. The surface should be a deep mahogany color with a set, dry bark.
Remove the roast from the smoker and wrap tightly in butcher paper or aluminum foil. Return to the smoker and continue cooking until the internal temperature reaches 195-202°F and a probe slides in with zero resistance (probe tender). This takes approximately 1-2 more hours.
Remove the wrapped roast from the smoker. Let it rest unwrapped on a cutting board for 20-30 minutes to cool slightly and redistribute juices.
Cut the chuck roast into 1-inch cubes using a sharp knife. Try to keep the pieces as uniform as possible for even caramelization.
Transfer the cubes to an aluminum foil pan. Pour the BBQ sauce and brown sugar over the top, plus the optional butter and honey if using. Toss until all cubes are evenly coated. They should be coated, not swimming in sauce.
Return the uncovered foil pan to the smoker at 250-275°F. Cook for 45-60 minutes, tossing once or twice. The burnt ends are done when the sauce has reduced to a tacky, glossy glaze and the cubes have darkened edges. The squeeze test: a cube should compress slightly without crumbling.
Remove from the smoker and rest for 10 minutes before serving.