Scrub the potatoes well leaving the skin on; then put the potatoes in a medium saucepan and add enough cold water to cover by 2 or 3 inches.

Over high heat, bring the water to a boil and then lower the heat to maintain a gentle boil. Depending on the size of the potatoes cook for about 20 to 30 minutes until tender. Drain the potatoes and let stand until cool to the touch then peel.

Into a medium saucepan, pass the potatoes through a potato ricer or mash well with a potato masher making sure not to leave any lumps.

Add the butter and over medium heat whip or stir until the butter is well incorporated and the mixture is smooth, about a minute. Remove from heat add the Parmigiano cheese and season with salt, white pepper, and a pinch or two of nutmeg if desired.

Beat one egg then along with the prosciutto and parsley stir into the potato mixture until all the ingredients are well mixed; then cool to room temperature.

Using about 3 tablespoons of the potato mixture for each Panzerotti, form into cylinders about 3 inches long. Press a stick of Provolone cheese lengthwise through one end of the panzarotto, Make sure to reseal the end.

Refrigerate the Panzerotti uncovered until firm, about 20 to 30 minutes. Note the Panzerotti can be prepared to this point and refrigerated covered for up to one day.

Beat the remaining two eggs well in a wide, shallow bowl and spread the breadcrumbs and flour out onto separate plates.

Dredge each panzarotto in flour lightly coating it and shaking off any excess. Then dip the floured panzarotto into the egg, coating all sides evenly. Finally, lay the Panzarotto in the breadcrumbs and roll to coat all sides and ends making sure the breadcrumbs are well adhered. Lay them out on a sheet of waxed paper.

Heat the vegetable oil in a heavy, medium skillet over medium heat to 350°.

Add about half the Panzerotti into the skillet and fry carefully, turning them until golden brown on all sides, about 4 or 5 minutes. Adjust the heat as necessary so the Panzerotti cook evenly.

Remove the Panzerotti with a slotted spoon and drain them on a paper-towel lined baking sheet.

Repeat with the remaining Panzerotti and serve hot.