¼ cup soy sauce
¼ cup tomato paste
¼ cup water
½ teaspoon cayenne pepper
¾ cup packed dark brown sugar
3-inch piece fresh ginger, peeled and roughly chopped
4 garlic cloves, peeled
4 pounds chicken wings, halved at joint (wing tips discarded)
Add ¼ cup of the brown sugar, 1 tablespoon of the soy sauce, the ginger, garlic and ¼ teaspoon cayenne pepper to the bowl of a food processor. Pulse until everything is finely ground and a paste-like mixture results. Transfer the mixture to your slow cooker then add the wings and toss to coat them with the paste.
Cook on low until the chicken is tender, 3-4 hours. Transfer the wings to a large bowl, leaving as much of the liquid behind as possible and discarding it when all of the wings have been removed. Let the wings cool for about 20 minutes. (At this point you can put the cooled wings in the refrigerator for up to 24 hours.)
Preheat your broiler and position one of the oven racks about 10-12 inches from the broiler. Line a rimmed baking sheet with aluminum foil, then place a wire rack inside the baking sheet. Spray the rack well with nonstick cooking spray.
In a medium bowl, whisk the water, tomato paste, remaining ½ cup sugar, remaining 3 tablespoons soy sauce, and the remaining ¼ teaspoon cayenne pepper. Add half of this sauce to the bowl with the wings and gently toss to coat. Place the wings on the rack, skin side up. (I fit all 4 lbs of wings on one rack – spacing was very minimal between the wings.) Broil until the wings are lightly charred, about 10-15 minutes. Remove the pan from the oven and flip the wings over. Brush the remaining sauce over them and return them to the oven. Broil for another 3 minutes, or until the sauce caramelizes.