Adapted from keyingredient.com
Split each chicken breast through the middle to make 2 pieces. Place plastic wrap over them and pound each one flat using a meat tenderizer/mallet until they are about a quarter inch thick. Season a good amount of salt and pepper on both sides of each piece. Place some flour on a plate and and dredge each piece of chicken in it.
Heat the oil over medium-high heat and when the oil is hot fry each piece of chicken for 3-4 minutes on each side until they are golden brown (this may require you to do this in 2 batches). Remove chicken and place them on your serving platter covering them with foil. carefully soak up any remaining oil with paper towels and discard.
Reduce the heat to medium and add butter and mushrooms. Saute mushrooms for 4-5 minutes making sure to season them with salt and pepper lightly. Add marsala wine, sherry, cream, and chicken stock allowing the liquid to reduce slightly – approx. 3 minutes. Pour mushrooms and sauce over chicken and serve. Enjoy!