1. Heat olive oil in large saute pan over medium-high heat.
2. When the oil is hot, dredge both sides of the chicken breasts in flour, shake off excess flour and place in pan.
3. Saute chicken, turning once, until lightly browned on both sides.
4. Transfer the chicken to a warm plate.
5. Drain all but a little bit of the oil and add mushrooms.
6. Saute the mushrooms until they begin to release their juices.
7. Add the Marsala wine, and scrape loose with a wooden spoon all browning residues on the bottom and sides of the pan.
8. Add butter, chicken broth, salt and pepper.
9. Cook until the liquid is reduced by half, approximately 5 minutes.
10. Place the chicken breasts back in the pan and cook until heated through.
11. Transfer the chicken breasts to warm serving plates, pour sauce over them and serve.