For the chicken with a creamy mushroom sauce, heat a large pan and add half of the oil. Season the chicken pieces with salt and pepper. Once the oil is hot, cook the chicken until golden-brown all over. Remove from the pan and set aside.
Add the pancetta to the pan the chicken was cooked in, and fry until crisp, then add the shallots, garlic and mushrooms and cook for 2-3 minutes.
Return the chicken to the pan and cook for two minutes.
Add the butter, Madeira, stock, cream and tarragon and simmer for 15-20 minutes. Remove the head of garlic before serving.
For the mashed potato, place the potatoes in a large pan of salted water and bring to the boil. Cook for 15-20 minutes, or until soft when tested with the point of a knife.
Drain the potatoes and place back into the pan to let the steam off. Mash and add the milk, cream and butter and mix until smooth.
Heat a pan of boiling water and blanch the beans, refresh in ice-cold water.
Heat a small frying pan and add a few knobs of butter, once melted add the beans and cook for a couple of minutes until the beans are coated in butter and tender.
To serve, place the mash into serving bowls with the chicken, sauce and green beans.