Preheat the oven to 220°C/425°F/Gas 7.
Bring a large pan of water to boil, add the potatoes and cook for around 20 minutes.
Pour breadcrumbs onto one plate and pour the beaten egg on to another.
Once potatoes are cooked, drain and mash them with a small knob of butter. Allow to cool.
Add the fish and mix well then add the lemon, spring onion, coriander and a little pepper.
Form 6 - 8 patties from the mixture and flatten by hand. The cooler the mash potato is when you do this; the easier it will be to form the patties.
Take each pattie and dip both sides into the egg and then into the breadcrumbs.
Heat a large frying pan with a generous glug of olive oil. When the oil is hot, carefully lower the fish cakes into the pan.
Cook for 5 - 7 minutes or until golden brown underneath and then carefully flip them over.
Fry for another 5 - 7 minutes or until golden on the bottom and heated all the way through.
Serve with a sprinkle of coriander.