Preheat the oven to 350 degrees.
Place the butter and oil in a large frying pan over medium heat. When hot, fry the chicken pieces for 2 to 3 minutes, until golden brown all over. Season well, then transfer to a casserole dish.
Add the bacon to the empty pan and fry for 2 minutes, or until browned. Transfer to the casserole dish.
Add the mushrooms, onions, and garlic to the empty pan and cook for 4 to 5 minutes, until glazed and golden brown. Stir in the tomato paste, wine, and stock; bring to a boil, then pour over the chicken in the casserole dish. Add the thyme and bay leaves, and then cover and bake for 40 to 45 minutes, until the chicken is cooked through.
Using a slotted spoon, transfer the chicken pieces to a plate, cover with kitchen foil and keep warm.
Remove the thyme and bay leaves from the sauce then bring it back to a boil. Add small pieces of the beurre manié to the boiling liquid (it is very important that the liquid is boiling or the sauce will be lumpy) and whisk rapidly until the sauce thickens. Taste and adjust the seasoning if necessary.
Return the chicken pieces to the casserole dish, stir gently to coat in the sauce, and garnish with the parsley. Serve with mashed potatoes.