How to Make It
In a medium bowl, whisk the chile and garlic powders with the oregano, celery salt, paprika, coriander, mustard powder, allspice, 1 tablespoon of salt and 1/2 tablespoon of pepper.
On a rimmed baking sheet, open up the lamb shoulder and rub the spice mix into the meat. Roll up the meat and tie at 1-inch intervals with kitchen string. Cover the lamb shoulder and refrigerate for at least 8 hours or overnight.
Remove the seasoned lamb shoulder from the refrigerator. Brush it all over with oil and season with salt and pepper; let the meat stand at room temperature for 30 minutes. Meanwhile, light a hardwood charcoal fire in a smoker. When the coals are ready, scatter the wood chips evenly over them. Attach the indirect cooking plate and heat the smoker to 225°.
Smoke the lamb fat side up for 6 to 7 hours, basting with some of the Sorghum Barbecue Sauce during the last 30 minutes. The lamb is done when an instant-read thermometer inserted in the center registers 185° and the meat is very tender; monitor the temperature throughout the cooking process and adjust the air valves as needed.
Transfer the lamb to a carving board and let rest for 20 minutes. Discard the kitchen string. Thinly slice the lamb across the grain and serve with the barbecue sauce.
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