COOK IT.
Place chuck roast in a glass baking dish. Season with Lone Star Brisket Rub, then cover with plastic wrap and refrigerate overnight.
The next day, remove the chuck roast from the refrigerator.
Preheat your grill or smoker to 225°F.
Once preheated, place chuck roast directly on the grill grate, then close the lid and smoke for 3 hours, spritzing with beef stock every hour.
Thinly slice the onion. Then add to the cast iron with 2 cups of stock. Set the roast in the cast iron, handling with care as it will be hot.
Increase the grill's temperature to 275°F and cook uncovered for an additional 2 1/2 - 3 hours, or until the internal temperature of the roast reaches 165°F.
Cover the roast with a cast iron lid or aluminum foil, and cook for an additional 2 1/2 - 3 hours, or until the internal temperature reaches 200°F and is fork tender.
Remove the chuck roast from the grill. Allow to rest for 15 minutes before removing it from the skillet to shred with meat claws.
Serve pulled roast beef in a hoagie roll with braised onions and pan jus (stock from the pan).