In a medium bowl, whisk together the pineapple juice, soy sauce, Marsala wine, brown sugar, sesame oil, garlic, chili powder, and red pepper flakes until the sugar is dissolved.
Put the chicken drumettes in a 1-gallon size, resealable plastic bag.
Add the pineapple liquid to the chicken and seal removing as much air as possible from the bag. Marinate the chicken for 3 hours in the refrigerator.
Put an oven rack in the center of the oven. Preheat the oven to 450 degrees F. Line a baking sheet with foil and spray it liberally with vegetable cooking spray.
Remove the chicken from the marinade and arrange in a single layer on the prepared pan. Season the chicken with salt, to taste, and bake until the skin is caramelized and very dark in spots, about 30 to 35 minutes.
Meanwhile, put the marinade into a small saucepan.
Whisk in the arrowroot or cornstarch, if using, and bring to a boil over medium heat (in order to kill bacteria). Reduce the heat to a low boil and cook until thick, about 5 minutes. Cool for 10 minutes.
Using a pastry brush, brush some of the cooked marinade over the chicken or pour it into a small bowl and serve on the side. Arrange the chicken on a platter, sprinkle with chopped cilantro and serve.
