Heat the butter, then in a wide pan fry the chicken evenly. Remove it and in the same pan, if needed - add a little oil, fry the chopped onion and sliced mushrooms. When nice and soft, add the chopped garlic and parsley.
Stir and top up with the cream. Simmer until slightly thickened and add the chicken steaks. Season with salt and pepper to taste and remove from the heat.