Boil 3cm potato chunks in water for 12-15 minutes until soft.
Drain, mash until smooth, season, and spread on a plate to cool.
Place fish, milk, bay leaf, and seasoning in a large saucepan.
Simmer briefly, then remove from heat and stand covered for 10 minutes.
Remove fish with a slotted spoon, reserve milk, and flake fish once cool.
Mix cooled mash with lemon zest, spring onions, and flaked fish.
Form six 3cm thick cakes and chill in the freezer for 20 minutes.
Prepare plates with flour, beaten eggs, and fresh breadcrumbs.
Dredge cakes in flour, dip in egg, and coat thoroughly with breadcrumbs.
Place coated cakes on parchment and chill until ready to cook.
Preheat oven to 200°C and fry cakes in oil for 3 minutes per side.
Transfer cakes to a tray and bake for 8-10 minutes until hot throughout.
Melt butter, stir in flour and reserved milk to create a smooth sauce.
Simmer sauce until thick, stir in parsley, and serve over the fishcakes.