Peel and boil the potatoes until cooked and soft. Ensure you drain all the liquid so they are dry. At the same time steam the cavolo nero leaves for a few minutes until soft, then drain.
In a medium bowl, mash the potatoes and make a smooth puree. Slice the cavolo nero very finely and mix through the hot puree.
Beat one of the eggs. Add the egg and the prosciutto to the potato mix.
Allow to cool down for 2 hours to stiffen up.
Place the mixture in a piping back and pipe a cylinder of around 1.5cm thickness. Cut this into 3-4cm pieces.
Beat the other egg and pour into a shallow dish for an egg wash.
Roll the potato bites in the egg wash, and coat in the breadcrumbs. Deep-fry them quickly in oil at 180°C.