1.Drop the tomatoes into boiling water for 10 seconds. Then cool under running water, peel, halve and squeeze out the seeds. Chop the flesh and keep aside.
2. Season the chicken with salt and pepper. Heat the oil and butter in a frying pan, and add the chicken pieces and garlic cloves when melted. Cook for 10 minutes until brown.
3. Pour in the Tarragon and White wine vinegars. Add tomatoes and season with salt, pepper and sugar. Cover and cook for 45 minutes on slow fire.
4. While the chicken is cooking, combine the cream and mustard in a small bowl. Remove the cooked chicken and keep aside. Strain the cooking juices through a fine sieve into a saucepan, and add the crushed garlic cloves. Boil over high heat until syrupy for about 5 minutes. Add the mustardy mixture and boil over high heat for 2 minutes to produce a thick creamy sauce. Pour over the chicken pieces and serve immediately.