Season the chicken and fry skin-side down in oil and 55g of butter until golden.
Brown the other side for 2 minutes and remove chicken from the pan.
Fry pancetta, carrot, mushrooms, shallots, and garlic in the remaining butter until golden.
Add wine and stir to deglaze the pan.
Return chicken to the pan with tomato purée, chicken stock, and tarragon.
Simmer for 30 to 40 minutes until the chicken is tender.
Stir in tomatoes and parsley, then season to taste.
Simmer for an additional 2 minutes.
Boil potatoes in salted water until tender.
Drain potatoes and dry them over low heat for 1 minute.
Mash potatoes thoroughly with butter and milk until smooth.
Season the mash with salt and pepper.
Serve chicken pieces topped with sauce alongside a portion of mash.