Gently heat half of the oil in a large, heavy-based frying pan. The oil should be hot, but not so hot that it scorches the floured chicken. Next, spread a layer of flour on a plate or a tray, and coat the chicken pieces evenly and thoroughly, shaking off any excess flour. This will add a golden-brown colour to the cooked chicken and help to thicken the sauce.
Put the floured chicken pieces into the hot olive oil, skin side down, and fry without moving the pieces until golden-brown underneath. This should take around 8-10 minutes. Next, turn the chicken and fry until browned on the other side.
Now finely chop the shallot and add to the frying pan, placing the shallot under the chicken so that the shallot cooks.
If you are using brandy, pour it in around the edge of the pan so that it runs underneath the chicken. Cook for 2-3 minutes to allow the alcohol to evaporate.
Add the wine in the same way, pouring it in around the sides of the pan, and cook for a further 2-3 minutes to allow the alcohol to evaporate and reduce the acidity.
Next, add the chicken stock pot and the tomato juice (with gravy browning if using). Shake the pan to gently work it in and turn the chicken pieces until fully coated in the liquid.
Bring slowly to the boil to allow the chicken stock pot to dissolve, then add the tarragon and simmer for 5 minutes.
While the chicken is simmering, take a separate frying pan and heat the remaining olive oil.
Slice the mushrooms and add to the second pan, then fry them for 3-5 minutes.
Next, add in the parsley and diced tomato, shaking the pan to mix everything in well.
Spoon the mushrooms, parsley and tomato over the chicken and garnish with sprigs of parsley, then serve.