Scoop out all the potato white into a mixing bowl and mash it with a fork until smooth.
Add the spring onions, egg, garlic, salt&pepper, chilli (if used) and enough polenta to have a thick batter. Fold in the coriander. Form small balls, then roll them in the leftover polenta and flatten them between your palms to create patties.
Heat some vegetable oil in a frying pan and add the patties. Cook for about 5 minutes on each side, flipping then once.
Transfer them to a plate and repeat with the remaining batter.
Alternatively bake/grill them in lightly oiled tin.
Serve with a dip or chilli sauce.