Preheat your oven to 300°F (150°C).
Pat the spare ribs dry with paper towels.
Mix brown sugar, paprika, garlic powder, onion powder, salt, black pepper, and cayenne pepper in a bowl.
Rub the spice mixture evenly over the ribs.
Place the ribs on a baking sheet lined with foil and cover with another piece of foil.
Bake in the preheated oven for 2 hours.
Remove the top foil and brush the ribs with barbecue sauce.
Increase the oven temperature to 400°F (200°C) and bake for an additional 30 minutes.
Let the ribs rest for 10 minutes before slicing.
Serve and enjoy your delicious spare ribs!