Preheat oven to 300 degrees then coat a grill pan or baking sheet with a rack inside with cooking spray.
In a small bowl, stir together all ingredients for dry rub until evenly combined. Pat ribs dry using paper towels then trim away excess fat and silver skin from both sides.
Season both sides of each rack of ribs generously with spice rub, using half of the rub for each rack. At this point, you may begin baking right away or cover and refrigerate for up to 24 hours.
Place ribs on prepared pan then bake 2½ hours. Begin checking ribs at about 2 hours and rotate if necessary for even cooking. If the edges of the meat are becoming too crispy and dark, cover the ribs loosely with a sheet of aluminum foil for remaining cook time.
When ribs are tender, remove from oven then brush top side with barbecue sauce. Return to oven and bake uncovered for an additional 20 minutes. Separate ribs by cutting between bones and serve with remaining sauce.
Don’t worry if you don’t use all the dry rub—it’s great on chicken or pork too! Simply seal what’s leftover in an airtight container and store it for up to 2 months.