Preheat smoker to 250 degrees Fahrenheit (we like cherry and apple).
Trim excess fat off the ribs and remove the membrane off the bone side of the ribs using a paper towel (it is slippery).
Rinse ribs under cold water, pat dry, and then coat both sides of ribs with the Dijon mustard.
Apply the dry rub to both racks, on both sides.
Place ribs meat side pointing up on the smoker. Plan to smoke for about three hours.
After the first 90 minutes, start spritzing every 20-30 minutes. Minimize how long you keep your lid open.
After your third hour, take 2 long strips of aluminum foil. Place ribs on them bone side down.
On top of the ribs, add the butter and agave nectar evenly over the meat side of the ribs (1 tablespoon of butter and nectar per rib, per side) and then wrap the ribs tightly. Place back onto the smoker meat side down for two more hours.
After the second hour, remove ribs from foil gently. The meat should be tender and bones showing. Place back on the smoker, meat side up, and glaze with your barbecue sauce. Cook one more hour, uncovered, (the last hour helps set the meat and give more flavor). When you remove after this last hour, glaze one last time before serving.