Preheat the oven to 200C.
Gently poach the fish in 300 ml of the milk seasoned with salt and pepper for 15 minutes..
Peel and boil the potatoes until tender, then mash with the milk and butter.
Boil the eggs for 10 minutes, run under cold water, then peel and slice.
Lift out the fish and place on a plate to cool a little. Flake the fish removing any bones.
Measure the warm milk used to poach the fish and top up to 500ml.
Mix cornflour with a little cold milk and add the cornflour mixture to the warm milk.
Cook until the sauce starts to thicken, season to taste.
Place the flaked fish in an ovenproof dish add the sliced hard-boiled eggs and top with the raw scallops. As they don't take long to boiled eggs and top with the raw scallops. As they don't take long to cook its better to put them in raw and they will be cooked in the oven.
Pour over the white sauce.
Cover the sauce with the mashed potatoes and fork up the potato to create crispy bits.
Place the dish on an oven tray and place in the oven for 15 minutes until the sauce is bubbling and the potato topping is golden brown and crisp on top