Place your chuck roast on a plate and pat dry with a paper towel.

Coat the roast with mustard. Set aside.

In a small mixing bowl, mix together the ingredients for the dry rub: salt, pepper, garlic powder, onion powder, celery seeds, and smoked paprika.

Sprinkle the dry rub on the chuck roast and slightly press into the roast. Make sure to cover all sides.

Place roast in an airtight container with a lid or a 9x13 inch pan covered with plastic wrap. Store in the fridge for 12 hours or overnight.

Prepare your BBQ for indirect heat. Plan for 8 hours+ cook time.

Bring your BBQ to 250°F.

Once at temperature, place the chuck roast on the grill. Close the cover and let it cook until it has reached an internal temperature of 150 to 160°F. This typically takes about 4 hours.

Cut 2 pieces of aluminum foil that are big enough to wrap the chuck roast.

Once the chuck roast reaches an internal temperature of 150 to 160°F, place it on the foil paper. Brush on 0.5 cup of barbecue sauce. Add the diced butter on top. Wrap the chuck tightly, being careful if using a probe.

Place back on the grill and close the cover.

Continue cooking until an internal temperature of 190 to 205°F is reached. Remove chuck from the grill and place on a cutting board. Let it rest for 30 minutes.

While the meat is resting, increase your BBQ temperature to 350°F.

Unwrap the chuck carefully. Dispose of the liquid in the aluminum foil. Cut into bite-sized pieces.

Place the pieces in an aluminum pan, pour the remaining BBQ sauce over them, and sprinkle with brown sugar.

Carefully mix to coat all the pieces. The meat will be very tender.

Once the BBQ has reached 350°F, place the foil pan on the grill.

Cook with the cover closed for 30 to 40 minutes, or until the sauce has thickened.