POUND chicken breasts between sheets of plastic wrap until about 1/4″ thickness.
SEASON with salt and pepper.
HEAT oil in a skillet over medium heat. Cook chicken breasts on medium heat for about 3 minutes on the first side, until lightly browned. Turn breasts over to cook other side, then add mushrooms to skillet. Cook breasts about 3 more minutes or until they reach 165F internal temperature and both sides are lightly browned. Continue to stir mushrooms. Add DRY Marsala wine around chicken pieces.
COVER and simmer for about 5 minutes.
REMOVE chicken breasts from pan and place in a serving plate. Add butter in the remaining sauce. Turn off heat, stir butter until it is melted and an emulsion is made.
DISTRIBUTE sauce over chicken breasts and serve immediately.
Note: Marsala wine is a fortified wine from Sicily and can be either dry or sweet; it’s used to create a rich caramelized flavor to the sauce. The wine is added to the chicken and mushrooms with butter to create the rich brown sauce for that authentic Italian taste. Chicken Marsala is best served with a starch like potato or over pasta.