Preheat oven to 300 degrees F. If necessary, remove silver skin from the back of spare ribs with a paper towel.
In a small bowl, mix to combine dark brown sugar, paprika, onion powder, cayenne, cumin, dried oregano, garlic powder, 3 tablespoons salt, and 2 teaspoons peppercorns. Place spare ribs on a large piece of tin foil. Rub smoked paprika into the ribs first, followed by the spice mix. Fold tin foil around ribs, crimping to secure.
Transfer to oven and cook until meat has pulled back from the bones, about 2 hours and 15 minutes.
Meanwhile, whisk to combine liquid smoke barbecue sauce in a small bowl.
Remove foil from ribs and pour any accumulated cooking juices into barbecue sauce. Whisk until smooth. Begin basting ribs with barbecue sauce and continue to bake, basting ribs every 15 minutes, for an additional hour, raising temperature to 400 degrees F for the final 15 minutes, until ribs are very tender and bones are nearly falling from the meat.
Slice ribs into pieces and serve with barbecue sauce.