Put the chicken breasts between 2 pieces of waxed paper and pound them out flat. Salt and pepper the chicken breasts.
Working in batches if necessary, heat half the butter to sizzling and cook the chicken breasts 3 minutes on a side until golden brown.
Place the browned chicken breasts on a foil lined cooking sheet and top each with a slice of Prosciutto, one or two sage leaves, and some of the cheese.
Place the chicken in the oven for 10-15 minutes to finish cooking.
In the same pan you used to brown the chicken breasts, cook the mushrooms in the remaining butter.
Once the mushrooms are cooked, stir in the wine and boil for two minutes, scrapping up the pan drippings with a wooden spoon.
Add the cream and boil for three more minutes until the sauce has thickened slightly.
Season to taste with salt and pepper.
Remove the chicken from the oven and serve with the mushroom sauce.