boneless skinless chicken breasts, each breast cut crosswise into 3 pieces • Salt and freshly ground black pepper • olive oil • butter, divided • chopped onion • cremini mushrooms, sliced • minced garlic • dry Marsala wine • mascarpone cheese (I used quality cream cheese) • chopped fresh Italian parsley leaves, plus whole sprigs, for garnish • Dijon mustard (possibly more, but taste it when it's ready) • dried fettuccine (I used Egg Noodles)