Heat the oven.
Preheat your oven to 300°F.
Mix the dry rub.
Stir together both sugars, onion powder, salt, smoked paprika, black pepper, ground mustard, cumin, cayenne, and nutmeg in a small bowl until evenly blended.
Remove the membrane.
Turn the ribs over and loosen the thin membrane on the underside with a small knife. Once you lift one edge, pull it away with your fingers. This step helps the seasoning reach the meat more effectively.
Prepare the foil.
Lay a long sheet of heavy-duty foil over a baking sheet, making sure it is long enough to fully wrap the rack.
Season the ribs.
Set the ribs on the foil bone-side up first. Rub part of the seasoning over the underside, then flip the rack and coat the meaty side with the remaining spice rub.
Seal and bake.
Fold and crimp the foil tightly around the ribs. Bake for 2 hours 30 minutes.
Make the glaze.
Stir the barbecue sauce and brown sugar together in a small bowl while the ribs finish baking.
Broil for color and flavor.
Remove the ribs from the oven and switch the oven to broil. Open the foil carefully, spoon the sauce over the top, and spread it evenly.
Finish the ribs.
Broil for 2 to 3 minutes, just until the sauce bubbles and starts to caramelize.
Rest and slice.
Let the ribs rest for 10 minutes before cutting between the bones and serving.