Coat the chicken in the flour, sprinkle lemon zest on them, season with salt and pepper and coat them again in the flour. Set aside.
In a large, wide frying pan/skillet, heat the olive oil and butter over medium heat.
Saute' the onions for 2 - 3 minutes until translucent. Add the garlic and saute' for another 2 minutes until aromatic.
Add the thyme to the pan.
Add the prosciutto to the pan and cook until reddish-brown and starts to curl up and shrivel. Add more butter if needed.
Add the mushrooms to the pan and cook until tender and beginning to brown. Add more butter if needed.
Add the chicken to the pan and cook until golden brown on all sides, about 3 - 5 minutes on each side. Then REMOVE the chicken (only) and begin making the sauce.
Add the Marsala wine to the pan, stir. Add the chicken broth, stir.
Bring it to a boil in order to start thickening.
Add the Mascarpone cheese or cream (you can substitute ricotta cheese) and continue to let it boil.
Add the chicken back into the pan and add the juice of about ¼th of a lemon.
Cover the pan and simmer for 20 minutes, checking on how it is thickening and how the chicken is coming along.
Taste and see what the dish may need: More mascarpone or cream? More butter?
If necessary for thickening: add 1 teaspoon of flour and stir it in; it will thicken immediately!
If necessary to thicken, partially cover up for another minute or two.
Place the chicken on a serving platter; sprinkle with a garnish of minced Italialn parsley. Ladel the sauce on top of the chicken. Serve with mashed potatoes and a bright green vegetable!
Buon Appetito!