Blanch the asparagus in boiling salted water for three minutes. Drain, reserving three tablespoons of the liquid.
Place each pork escalope between two sheets of cling film and pound with a meat mallet to make a 12x18cm/5x7in rectangle. Season lightly with salt and pepper. Trim both the mortadella and cheese slices to a size just a little smaller than each escalope.
Cover each piece of pork with a slice of mortadella, then a slice of cheese. Place an asparagus spear in the centre, running across the shortest width, with the tip slightly overhanging the pork at one end. Place another asparagus spear alongside but with its tip overhanging the other end. Roll each pork slice up tightly and tie in place at each end with kitchen string. Roll in the seasoned flour to coat.
Heat two tablespoons of the butter with the olive oil in a frying pan. Fry the rolls over low heat for about 10 minutes, turning frequently until golden and tender. Transfer to a hot serving dish and keep warm.
Add the Marsala and the reserved asparagus liquid and bring to the boil quickly. Simmer for 3-4 minutes scraping up the bits from the base of the pan. The juices will reduce and darken. Taste for seasoning, and add a little more butter if you want a richer sauce. Then spoon over the pork rolls and serve immediately.
