1. Preheat the oven to 150°C/130°C fan/gas mark 2.
2. Place a casserole dish over a medium heat and add the oil to heat up. Dust the chicken in the flour, then add to the pan and fry for 8 minutes until golden all over.
3. Remove from the pan, reduce the heat and add the remaining oil, onions, leek and celery. Cook for 5 minutes, until soft, then add the pancetta and cook for a further 5 minutes on a slightly higher heat.
4. Stir in the garlic and wine, increasing the heat for a couple of minutes until the wine has reduced by two thirds.
5. Add the stock, stir well and bring back up to the boil, seasoning generously with black pepper. Return the chicken to the pan, arranging the pieces skin-side up across the dish.
6. Place in the oven and cook for 80 minutes, keeping an eye on the liquid level and topping up with a little extra stock if required.
7. After this time, add the peas straight from the freezer and increase the heat to 200°C/180°C fan/gas mark 6. Remove the lid from the dish and return to the oven uncovered to brown the skin.
8. Stir in the herbs and allow the casserole to sit for 5 minutes before dividing between bowls to serve.