For the oven-roasted ribs: Preheat the oven to 350 degrees F.
Pass the brown sugar, paprika, salt, cocoa, cayenne and cumin through a sieve into a bowl to remove lumps. Rub on both sides of the pork. Place the pork on a rack on a sheet tray and bake for 1 1/2 to 2 hours.
For the smoked barbeque sauce: Heat the vegetable oil in a medium pot over medium heat. Add the onion and garlic and cook about 5 minutes. Stir in the ketchup, vinegar, brown sugar, steak sauce, Worcestershire, molasses, mustard, salt, celery seed and 1 cup water. Bring to a boil, then reduce the heat to medium low and simmer until the onion is tender, about 15 minutes. Stir in the liquid smoke. Strain the sauce, pressing on the solids to extract any liquid.
Remove the pork from the oven and brush with some of the smoked barbeque sauce. Place back in the oven at 425 degrees F and cook for another 15 to 20 minutes.