Make the mashed potato first (using the mash ingredients) and allow to cool.
Add the egg, green onions prosciutto and garlic to the cooled potato.
Take two tablespoons of potato mixture and form into a patty. Dip the patty into the extra egg and press into the breadcrumbs until well coated in crumbs. Repeat this process with the remaining mixture.
Using a medium heat, heat enough oil to cover the base of a large non-stick fying pan, cook the patties in batches for 3-4 minutes on each side or until a golden brown colour.