Combine the paprika, black peppercorns, coriander seeds, cumin seeds, garlic powder, onion powder, nutmeg and cayenne in a spice grinder. Process until a fine powder is formed, approximately 30 seconds.
Pat the ribs dry and turn bone-side up. Trim excess fat and, if one end of the ribs is especially narrow, trim meat and bone to ensure even cooking. Remove the membrane on the underside of the ribs by inserting a rounded utensil, an upside-down spoon works well, between the membrane and the meat at one end of the slab. Carefully work the spoon under the membrane to loosen but not tear. Once enough has been loosened, use a paper towel to hold onto the membrane as you slowly pull it down the slab to remove.
Sprinkle the ribs on both sides with the salt and brush both sides with the mustard. Sprinkle two-thirds of the spice mixture on the meat side of the ribs and the remaining third on the bone side.
Once the smoker has reached 225 degrees F, add the wood chips or chunks and the ribs to the smoker.
Smoke for 4 to 5 hours then test for doneness. There are four criteria that should be met in order for ribs to be done. First, the internal temperature of the meat should be 185 to 190 degrees F. Second, pick up each slab from the center with tongs and it should droop into a u-shape and crack slightly. Third, while holding with the tongs, and bouncing gently, the surface of the ribs should crack slightly. Lastly, the meat should pull easily off the bone but not fall off. If ribs pass all tests, remove them from the smoker and wrap in heavy-duty foil and rest for 15 minutes. If not, continue smoking for 45 minutes to 1 hour and test again until done.