Trim the scaloppine into rectangles about 3 or 4inches on one side and 5 to 6inches on the other. If some of the slices don’t yield quite those measurements, it won’t affect the flavor of the involtini, but try to keep them reasonably similar in size.
Cut away all the green tops of the leeks, and slice the remainder lengthwise in half. Wash in a few changes of cold water.
Cook the leeks in boiling salted water until very soft when tested with a fork. The time depends on the youth and freshness of the leeks, but it will be in excess of 30 minutes. Drain thoroughly.
Lay the scaloppine flat on a work surface and cover each with a layer of leeks. Top with a few slivers of Parmesan and add salt and liberal grindings of black pepper. Roll up the scaloppine and fasten each one with a toothpick, inserting it lengthwise so that it lies parallel to the roll.
Choose a skillet large enough to accommodate the veal rolls later in a single layer without overlapping. Put in the butter and oil and turn on the heat to medium high. When the butter foam begins to subside, quickly turn the rolls over in the flour, and slip them into the pan. Turn the heat up to high and cook the meat for about 5 or 6 minutes, turning it until it becomes colored a dark brown over most of its surface.
Transfer the veal rolls to a plate using a slotted spoon or spatula. Add the wine to the pan and, as it bubbles, scrape loose the cooking residues with a wooden spoon. Boil the wine down to about half its original volume to obtain a fairly dense, dark juice.
Return the veal rolls to the pan, turn them over and over in the pan juices for about 1 minute, then transfer the entire contents of the pan to a very warm platter and serve at once.