Heat a li¢le oil in a large pan with a lid. Add the langoustines and cook for 2–3 minutes. Remove and set aside. Season the chicken and add to the pan. Brown all over then remove and set aside. Add a li¢le more oil and a good knob of bu¢er to the pan. Fry the onions very, very gently for 20–30 minutes until really so€ft and caramelised. Add the tomatoes, garlic and bay leaf and cook for 10 minutes more. Add the wine and vinegar and bubble for a minute then add the stock and tarragon. Return the chicken and any juices to the pan, cover and simmer for 15 minutes until the chicken is almost cooked. Add the langoustines to the pan and cook for a couple of minutes more. Serve with crusty bread to mop up the juices.