Tie bouquet garni together with kitchen string, or in a cheesecloth bag. Preheat oven to 160ºC . In a deep ovenproof skillet with a lid, brown bacon over medium-high heat, about 3 minutes, and transfer to paper towels to drain. Pour off any fat in the pan. Add half tb. of the peanut oil to the pan and brown chicken over high heat, about 3 minutes per side. Transfer the chicken to a plate, season with salt and pepper and set aside. Add the remaining half tb. oil to the pan, reduce heat to low and add onions. Cook, stirring occasionally, until the onions are very tender and golden, about 25 minutes. Stir in garlic and cook for 1 minute. Pour in cider and calvados or brandy and bring to a boil. Add prunes, bouquet garni, and the reserved bacon and chicken. Cover and bake until the chicken is very tender and no longer pink inside, 45 minutes to 1 hour. Remove the bouquet garni. Taste and adjust seasonings before serving.