How to Make It
In a bowl, combine the veal, apple, walnuts, cheese, egg, bread crumbs and sage. Season with salt and white pepper and mix with your hands until combined. Shape into 12 croquettes about 2 inches long and 1 inch thick.
Spread some flour on a plate. Roll the croquettes in the flour, tapping off any excess. In a large skillet, melt the butter in the olive oil until shimmering. Add the croquettes and cook over moderate heat until browned, 2 to 3 minutes per side. Transfer the croquettes to paper towels to drain.
Add the Marsala to the skillet and cook over moderately high heat for 2 minutes, scraping up any browned bits from the bottom of the pan. Arrange the croquettes on 4 plates, spoon the sauce on top and serve at once.