Step 1

Place 2 tablespoons packed brown sugar, 1 tablespoon paprika, 1 tablespoon kosher salt, 1 1/2 teaspoons garlic powder, and 3/4 teaspoon coarsely ground black pepper in a small bowl and stir to combine.

Step 2

Pat 2 racks baby back ribs dry with paper towels. Flip the racks over so that the bones are facing up. Pry a finger or table knife between the silvery membrane and the ribs to start pulling up the membrane — sometimes it's easier to do between two of the rib bones. Once you have a piece of membrane pulled up, you should be able to easily pull the whole membrane off.

Step 3

Cut the racks into 3 to 4 bone sections: Hold the rack upright and guide the knife through the meat between the bones.

Step 4

Arrange the racks meaty-side up. Evenly sprinkle the ribs with the spice rub and press it into the meaty parts. Transfer to a 6-quart or larger slow cooker, standing them upright and arranging them parallel to each other as best as you can. Add 1/2 cup water.

Step 5

Cover and cook until the ribs are knife-tender but not falling off the bone yet, 3 to 4 hours on HIGH, or 4 1/2 to 6 hours on LOW. Heat the broiler or outdoor grill when the ribs are almost ready.

Step 6

Option 1: Broiling. Arrange a rack in the upper third of the oven and heat the oven to broil. Line a rimmed baking sheet with aluminum foil. Transfer the ribs meaty-side up to the baking sheet in a single layer. Brush generously with 1/2 cup barbecue sauce. Broil until the sauce is bubbling and beginning to char in spots, 2 to 4 minutes.

Step 7

Option 2: Grilling. Heat an outdoor grill for direct, medium heat (about 350ºF). Transfer the ribs meaty-side up to a baking sheet in a single layer. Brush with 1/2 cup barbecue sauce. Place the ribs on the grill meaty-side up. Cover and grill until the sauce is bubbling, 5 to 10 minutes. Flip the ribs, cover, and grill until the meaty side begins to char in spots, about 5 minutes more.

Step 8

Cut into individual ribs if desired and serve with more barbecue sauce on the side.