Using a toothpick, secure a sage leaf and slice of prosciutto to each veal escalope.
Melt 3 tablespoons of butter in a frying pan over medium high heat. Place the veal slices in the pan and cook for two minutes on each side. Add the wine and season with salt and pepper. Continue cooking until the wine has nearly reduced. Transfer the veal to serving plates.
Add the last tablespoon of butter and one tablespoon flour to the pan; whisk constantly, scraping up any bits of meat stuck to the pan. Spoon sauce over the veal and serve.