Optional step: Remove the membrane from the ribs for more tender results. Use a paper towel to grip and peel it off.

Preheat your 8-quart slow cooker on low heat setting. Cut the ribs in half between the bones and set aside.

Mix brown sugar, smoked paprika, black pepper, salt, garlic powder, onion powder, and cayenne pepper in a small bowl to prepare the dry rub.

In a separate bowl, combine 1 cup of barbecue sauce with 2 tablespoons of water to thin slightly.

Layer one half rack of ribs into the slow cooker, meat side up, and sprinkle with half of the dry rub. Drizzle half of the barbecue sauce mixture on top.

Repeat with the second half rack, meat side up, adding remaining dry rub and barbecue sauce.

Cover with lid and cook on low for 6 to 8 hours or on high for 3 to 4 hours. Ribs are done when meat easily pierces with a fork between bones.

Once cooked, optionally transfer ribs to a lined baking sheet and broil for a few minutes until caramelized. Brush with additional barbecue sauce if desired.

Allow ribs to rest for 10 minutes before slicing and serving.