Step 1

Preheat the oven to 170°C.

Step 2

Place fish in a baking dish, season with salt and pepper and pour over 400ml milk. Cover with foil and bake for 15 minutes until fish flakes away slightly when pressed with a fork. Remove fish, reserving milk. When cool enough to handle, flake fish into bite-sized pieces.

Step 3

Cook potatoes in boiling salted water until tender. Drain and keep warm. Melt half the butter in a saucepan, stir in flour and cook over low heat for 2-3 minutes.

Step 4

Slowly add reserved milk and continue to cook until thickened. Add fish, peas, parsley, egg, lemon juice, salt and pepper.

Step 5

Mash the potato with the remaining 50ml milk and the remaining butter until smooth, then season. Pile the fish mixture into a 1 litre-capacity baking dish, spoon the mash on top and smooth with a spatula. Trace a pattern into the mash with the tines of a fork and sprinkle with grated cheese. Bake for 20-25 minutes until golden.