To make mushrooms, Remove stems from mushrooms and chop fine.
Put proscuitto, stems, onion, and garlic in a frying pan and saute in small amount butter or olive oil.
Cook until onion is soft, then drain.
Stir in remaining ingredients.
Stuff mushroom caps with this mixture.
Bake on a cookie sheet at 375F degrees for 10 minutes.
To make chicken and sauce, Season chicken with salt and pepper and grill. Set aside.
In the meantime, coat large skillet lightly with olive oil and set over medium-high heat. Add proscuitto and cook just until crisp and lightly browned. Combine Marsala, broth and corn starch. With pan over medium-high heat add the Marsala mixture and scrape up the browned bits from the bottom of the pan.
Cook Marsala mixture until it is reduced by one quarter. Stir in cream and simmer until you get a nicely thickened sauce.
Add chicken to the pan and turn to coat and reheat for a minute.
Place chicken on a platter and top with one or two stuffed mushrooms.
Serve with the sauce over top and a sprinkle of parsley.