For the sauce:
1 1/2 cups organic ketchup
1/2 cup packed dark brown sugar
3 medium garlic cloves, finely chopped
3 tablespoons cider vinegar
3 tablespoons Worcestershire sauce
3/4 teaspoon freshly ground black pepper
1/2 cup water
3 pounds Yellow Bell Farm boneless, skinless chicken breasts or bone-in, skin-on chicken pieces
Kosher salt and pepper
For the sauce: Combine all of the ingredients in a small saucepan over high heat. Bring to a boil, stirring until completely incorporated. Reduce the heat to low and gently simmer until the flavors have mingled and the sauce has thickened enough to coat the back of a spoon, about 30 to 40 minutes. Remove from the heat and let cool to room temperature. If not using right away, cover and refrigerate the barbecue sauce for up to 2 weeks.
Heat grill to medium (about 350°F to 450°F) and rub the grates with a towel dipped in oil. Pat the chicken pieces dry with paper towels. Coat them on all sides with the measured oil, and season with salt and pepper. Place the chicken on it (skin-side down if using skin-on), close the grill, and cook until grill marks appear on the bottom of the chicken pieces, about 5 minutes. Flip the chicken over, close the grill, and cook until grill marks appear on the second side, about 5 minutes more.
Reserve 1 cup of the barbecue sauce in a separate bowl. Flip the chicken again and brush about a quarter of the remaining sauce on the chicken pieces. Close the grill and cook for 5 minutes. Flip and brush the chicken, and continue to flip and brush every 5 minutes, until the meat near the bone is no longer pink, about 10 to 15 minutes more (about 25 to 30 minutes total cooking time). Remove the chicken to a clean serving platter and serve immediately, passing the reserved bowl of barbecue sauce on the side. Enjoy!