Preheat your oven to 300°F and line a baking sheet with aluminum foil.
Trim any excess fat from the spare ribs and pat them dry with a paper towel. Remove the membrane from the back.
In a small bowl, whisk together the brown sugar, paprika, garlic powder, thyme, salt, and pepper.
Rub the seasoning mixture thoroughly over all sides of the ribs. Cover and refrigerate for 30 minutes to marinate.
Place the marinated pork spare ribs on the prepared baking sheet, meaty side up. Cover tightly with foil and bake for 2 1/2 to 3 hours, or until the ribs are very tender and an instant-read thermometer reads 195-203°F in the thickest part.
Remove the foil, drain off excess fat if needed, and brush barbecue sauce over both sides. Return to the oven uncovered for 20–30 minutes, until the sauce caramelizes and the ribs are sticky.
Remove from the oven and cover loosely with foil. Rest for 10–15 minutes before slicing.
Cut between the bones and serve warm, brushing with more sauce if desired.