Place the chicken breasts between two large pieces of cling film and pound as flat as possible with a rolling pin.
Put the flour on a shallow plate and season liberallly with salt and pepper.
Dip the chicken breasts into the flour to lightly coat and set aside.
Heat one tablespoon each of butter and olive oil in a frying pan. Fry the chicken over medium-high heat for 2-3 minutes on each side until golden. Transfer to a plate and set aside.
Wipe the frying pan with some kitchen towel. Heat the remaining butter and oil and fry the shallots and garlic over low heat for five minutes, stirring so that they don't stick.
Add the mushrooms and cool for 2-3 minutes.
Add the wine and turn heat to high. Cook for 10 minutes or until the liquid is reduced by about half.
Reduce the heat and stir in the stock and mustard powder. Add the chicken breasts and cook for 10 minutes.
Stir in the cream or creme fraiche and check the seasoning.
Serve sprinkled with parsley and grated Parmesan with roast potatoes, mash or rice.