Melt butter in a large frying pan over medium high heat. Add escalopes and increase the heat to high. Cook for 4-5 minutes per side or until browned. Remove veal from the pan, salt to taste and keep warm.
In the same pan, add 1 tablespoon olive oil and cook the mushrooms over medium high heat. When they are tender, remove from the heat and season with slat and pepper to taste.
Turn the heat to low and add the marsala wine to the pan, scraping the bottom of the pan to loosen any bits of veal and mushroom stuck to the pan.
Spoon the sauce over the veal and mushrooms and serve hot. Top with freshly chopped parsley.