In a Saucepan melt the butter over a medium heat, stir in the flour and cook out for a few minutes. Gradually add the milk stirring continuously until thickened and add the grated cheese.
Pour the sauce into a ice cube tray and pop in the freezer.
Boil the potatoes in a pan of salted water for 20 minutes until tender. Drain and allow the excess moisture to steam off for a couple of minutes.
In a bowl, mash the potatoes and stir in the salmon, lemon zest, parsley and season generously. Divide the mix into 8 equal portions and form around a cube of the frozen cheese sauce, pop into the fridge to firm up for 10-15 mins.
Dip the chilled fish cakes into the flour, then the egg and finally into the breadcrumbs. Repeat for the rest.
In a heavy bottomed frying pan heat 2cm of oil over a medium heat. Working in batches fry the fishcakes for 3-4 minutes each side until crispy and golden. Serve with a green salad.