1. Preheat your oven to 275°F (135°C). Line a large baking sheet with foil for easy cleanup. 2. In a small bowl, combine the brown sugar, smoked paprika, garlic powder, onion powder, salt, black pepper, and cayenne pepper (if using) to make your rub. 3. Pat the ribs dry with paper towels. Remove the membrane from the back of the ribs if it hasn't been done already. Rub the spice mixture generously all over both sides of the ribs. 4. Place the rubbed ribs on the prepared baking sheet. You can tightly cover the pan with another sheet of foil to lock in moisture, or bake uncovered for a slightly crispier exterior. 5. Bake for 3 to 3.5 hours, or until the ribs are very tender and the meat easily pulls away from the bone. The exact time will depend on the thickness of your ribs. 6. For the last 15-20 minutes of cooking, remove the foil (if used) and brush the ribs generously with your favorite BBQ sauce. You can also increase the oven temperature to 350°F (175°C) or briefly broil for a caramelized glaze (watch carefully to prevent burning). 7. Remove from the oven, let rest for 5-10 minutes, then slice between the bones and serve immediately.