For the chicken:
For the sauce:
1 large disposable aluminum roasting pan (for charcoal) or 2 disposable aluminum pie plates (for gas)
To prep the chicken, combine the sugar, salt, onion powder, garlic powder, paprika and cayenne in a small bowl. Whisk until well blended. Arrange the chicken in a single layer on a baking sheet and sprinkle both sides evenly with the spice rub. Cover with plastic wrap and refrigerate for at least 6 hours or up to 24 hours.
To make the sauce, combine the ketchup, molasses, vinegar, Worcestershire, mustard and pepper in a bowl or a liquid measuring cup. Whisk to blend. In a medium saucepan, heat the oil over medium heat until shimmering. Stir in the onion and garlic. Cook until the onion is just softened, 2-4 minutes. Stir in the chili powder and cayenne and cook just until fragrant, about 30-60 seconds. Stir in the ketchup mixture and bring to a boil. Lower the heat to medium-low and simmer gently for about 5 minutes. Reserve ¾ of the sauce for basting the chicken, and the rest will be additional for serving.
To prepare a charcoal grill, open the bottom vent halfway. Place the aluminum pan filled with 3 cups of water on 1 side of the grill. Light a large charcoal chimney filled with charcoal. When the top coals are partially covered in ash, pour evenly over the other half of the grill (on the side opposite the aluminum pan). Place the cooking grate, cover the grill, and open the lid vent halfway. Heat grill until hot, about 5 minutes.
To set up a gas grill, place 2 disposable pie plates directly on 1 burner (opposite the primary burner). Fill each with 1½ cups of water. Turn all the burners to high, cover, and heat the grill until hot, about 15 minutes. Reduce the heat of the primary burner to medium-high and turn off the other burners. Maintain the grill between 325˚ and 350˚ F, adjusting the burner as needed.
Clean and oil the grate. Place the chicken, skin side down, over the hotter part of the grill and cook until browned and blistered in spots, 2-5 minutes. Flip the chicken and cook until the second side is browned, 4-6 minutes. Move the chicken pieces to the cooler part of the grill and brush both sides with 1/3 cup of the reserved sauce. Arrange the chicken skin side up, larger pieces closer to the hotter side of the grill. Cover (with vent over the chicken if using charcoal), and cook for 25 minutes.
Brush both sides of the chicken with the remaining reserved sauce and continue to cook, covered, until breasts register 160˚ and leg quarters register 175˚ F on an instant read thermometer, about 25-35 minutes longer. Remove the chicken to a serving platter, tent with foil, and let rest 10 minutes. Serve, passing the additional sauce (not the sauce that was in contact with raw chicken).
Note: Since this recipe is a bit involved, you might as well go ahead and make a full batch even if you aren’t serving 6-8 people. It freezes well (we shredded it and tossed with a bit of the additional sauce), and is great later for sandwiches, pizza, etc.