Heat the oven to 180C/fan 160C/Gas 4. Heat the olive oil in a large pan or flameproof casserole over medium to high heat. Season the chicken with salt and pepper and fry until crisp and golden all over.
Remove the chicken from the pan, then tip out the fat, wipe the pan clean, and add the butter. Stir in the tomato purée and cook over medium heat for 2 minutes, then add the garlic and cook for 1 minute.
Add the vinegar and reduce until it has all but disappeared. Add the wine and reduce by a third. Pour in the chicken stock and bring to a simmer, then return the chicken to the pan. Cover with a lid and transfer to the oven. Cook for 20 minutes or until the chicken is cooked through.
Meanwhile, quarter the tomatoes and scoop out the seeds. Cut the tomato flesh into small dice and set aside.
For the mash, cook the potatoes in a pan of lightly salted water for 15 minutes until tender. Drain and pass through a potato ricerback into the saucepan and stir over a low heat to dry out.
Gently warm the cream in a small pan until just boiling, then remove from the heat. Gradually beat a little butter and then a little of the cream into the mash. Keep adding and beating until the potato is soft and creamy, then season with salt and pepper to taste.
Remove the pan from the oven, lift out the chicken pieces and keep warm while you finish the sauce. Strain the sauce through a sieve into a clean pan and bring back to the boil. Whisk in the mustard and cream, then simmer to reduce and thicken slightly. Check the seasoning, then add the diced tomato and tarragon. Pour the sauce over the chicken and serve with the mash.
Recipe from James Martin's French Adventure (Quadrille)
Image: Peter Cassidy