If you start with whole spareribs, they'll need to be trimmed. Cut the loose point off the the small end to square it up. Remove the remains of the the skirt, which is located near the center of the bone side of the slab. Remove enough of the sternum (the thickest part of the slab) to make the ribs close to an even width from end to end. Trim off any loose flaps of meat and fat.
The tough membrane on the bone side of the ribs needs to be removed next. Slip the blade of a butter knife or a screwdriver under the membrane in one spot to loosen it. Grasp it using a paper towel and rip it off of the slab. If it tears, pry up another flap and keep peeling until the job is done. You may see thick deposits of fat now, that should be scraped off.
Season the ribs next with a dry rub mixture. Combine two tablespoons of paprika, two tablespoons of onion powder, two tablespoons of white sugar, one tablespoon chili powder, one tablespoon of ground black pepper, two teaspoons of celery salt, one teaspoon of garlic powder, one teaspoon of powdered mustard and one-half teaspoon (or to taste) of cayenne pepper. Season both sides of the slabs, stack them, and wrap them in foil. Let them rest for an hour at room temperature, or overnight in the fridge.
Smoke the ribs at 225 degrees Fahrenheit for two hours, then wrap them in foil. Continue cooking for another two hours at 300 degrees, then check for doneness. The smoked pork spare ribs should be tender and moist. If not, cook another hour, or until the ribs are done.