Chicken chasseur

1) Heat half of the butter and the oil in a heavy bottomed pan and brown the chicken pieces on all sides. You may need to do this in batches. .
2) Remove the chicken and set aside
3) Add the remaining butter to the casserole and sauté the onions and shallots for 3-4 minutes.
4) Add the garlic, tomatoes and mushrooms and cook for 3 mins, then stir in the tomato puree. 
5) Sprinkle over the flour and stir. 
6) Add the wine and bring to the boil, allow to reduce for about 5 minutes.
7) Now add the thyme, tarragon, bay leaf and the stock.
8) Add the reserved chicken to the pot bring to a simmer, cover and cook for 1 hour or until the chicken is cooked.
9) Serve the chicken with some lovely mashed potatoes.