Preheat the oven to 200°C.
Boil the chopped potatoes in a large saucepan until tender.
Drain the potatoes and mash them with 25g of butter until smooth.
Poach the fish fillets in a frying pan of boiling water for 6 minutes.
Flake the cooled fish and mix it into the mashed potatoes.
Shape the mixture into four large patties.
Coat each patty in seasoned flour, then beaten egg, and finally breadcrumbs.
Refrigerate the fishcakes for 20 minutes to firm up.
Place fishcakes on a lined tray, drizzle with olive oil, and bake for 20 minutes.
Sauté sliced onion in 25g of butter until tender.
Add the peas, crush them lightly, and stir in the cream cheese until melted.
Serve the hot fishcakes with the creamy peas.