Melt 2 T. butter in a large seasoned cast iron skillet or non-stick skillet over medium-high heat. Add mushrooms; cook 8 minutes or until browned and tender, stirring twice. Add garlic; cook 1 minute, stirring to incorporate. Transfer to a bowl.
Combine flour, 1/2 t. salt, and 1/4 t. pepper in a shallow dish; dredge veal in flour mixture, and set aside.
Melt 1 T. butter in skillet over medium-high heat. Add half of veal, and cook 1-1/2 minutes on each side. Transfer to a platter; keep warm. Repeat procedure with remaining 1 T. butter and veal, reserving drippings in skillet.
Add Marsala wine to skillet, stirring to loosen particles from bottom of skillet. Add beef stock, and boil 1 minute, stirring until thickened. Stir in parsley, remaining 1/2 t. salt and 1/4 t. pepper, mushroom mixture and any accumulated veal juices from platter; cook, stirring constantly, 1 minute. Spoon sauce over veal.