Cut the chicken breasts in half horizontally to make them thinner. One by one place between plastic wrap or parchment paper and pound gently to uniform 1/2" thickness.
Press a slice of prosciutto to top of each piece of chicken, then place a sage leaf onto prosciutto.
Mix flour, salt & pepper in a shallow bowl. Lightly dredge both sides of each chicken piece. Set aside.
In a large skillet, heat olive oil over medium heat. Cook chicken in batches, prosciutto side down until browned, about 5 minutes, then flip and cook through. Remove to plate and cover with foil to keep warm while preparing mushroom pan sauce.
For the Mushroom Pan Sauce
Using same skillet, saute mushrooms and shallot over medium heat until mushrooms are golden, then add garlic saute additional minute.
Add white wine and deglaze pan, stir scrapping any brown bits. Allow to wine to cook down until almost gone, then add chicken stock and cook over high heat until it becomes a thin gravy. Finish with butter, parsley and sage. Season with salt and pepper to taste.
To serve, remove pan from heat. Return chicken pieces to pan and spoon sauce over top. Serve on a platter family-style. Enjoy!!