Set your smoker for 225-250 degrees Fahrenheit according to manufacturer instructions, using hickory or applewood.
Mix together all the dry rub ingredients into a small bowl and set aside.
While the smoker is reaching the desired temperature, remove your ribs from the refrigerator. Pat them dry with paper towels, then remove the thin membrane from the bone side of the ribs.
Coat the ribs on both sides in a thin layer of yellow mustard. Sprinkle the dry rub over both sides of each rack, making sure that the majority of the rub is on the meat side of the ribs.
Place the prepared ribs onto the smoker once the smoker has reached the proper temperature. Smoke for 3 hours.
Open your smoker, quickly and carefully wrap each rib rack in aluminum foil using tongs and heatproof gloves, then return them to the smoker. Smoke for 1 hour if you want a little resistance to the tooth, or two hours if you want the meat to completely fall off the bone when you bite into them.
After your desired time is up, quickly remove the foil. Be careful, as the ribs are fragile by this point. Put them back on the smoker for a hour. If you want, you can brush them with barbecue sauce about 45 minutes in.
Remove from the smoker very carefully with a grill spatula and tongs. Serve immediately, or to transport, wrap the ribs in foil, then wrap them in kitchen towels. Put them in a cooler and top with more towels. This will keep them warm if you need to drive to your cookout.
Macros per serving, (6 servings) using spare ribs and 6 tablespoons of barbecue sauce for the recipe: 1326 calories, 2 grams net carbs, 71 grams protein, 108 grams fat.