1. Trim any excess fat from the chicken and season them with salt and pepper. Heat 1 tbsp of the oil in a large flameproof casserole over medium-high heat. In batches, add the chicken and cook, turning once, for about 4 minutes, until browned. Transfer to a plate. Pour the fat out of the pan.

2. Add the remaining 1 tbsp oil and heat over medium-low heat. Add the onion and garlic and cook, stirring often, about 3 minutes, until softened. Stir in the wine and boil for 1 minute, scraping up the browned bits in the pan. Stir in the tomatoes, stock, mushrooms, celery, tomato paste, rosemary, and sage and bring to a simmer.

3. Return the chicken to the pan and cover. Simmer for 40 minutes, or until the chicken shows no sign of pink when pierced at the bone. During the last 10 minutes, add the olives. Serve hot.