Chicken with Peanut-Butter Barbecue Sauce

Heat the oil in a large skillet over medium-high heat. Season the chicken with salt and pepper and place it in the pan in a single layer (if necessary in portions). Cook, turning frequently, until golden brown, about 5 minutes. Put it in the slow cooker. Repeat with the remaining chicken.Add all but 1 tablespoon of the fat from the pan. Add the onion and cook, stirring frequently, until soft, about 3 minutes. Add the garlic; simmer for another 1 minute. Add the barbecue sauce and peanut butter. Stir, scraping the browned pieces from the bottom of the pan, until they are slightly thickened, about 2 minutes. Pour the sauce over the chicken and stir to coat it.Cover and cook until the chicken is cooked through, 2 1/2 to 3 1/2 hours, over low heat. Remove the lid, set the heat to high, and cook, turning the chicken frequently, until the sauce thickens, about 20 minutes. Serve immediately.