Preheat the oven to 190°C / fan oven 170°C / Gas Mark 5. Grease an ovenproof baking dish with a small knob of butter.
Cook the potatoes in lightly salted boiling water for about 20 minutes, until tender. At the same time, cook the courgettes for about 5 minutes, then drain them well.
Meanwhile, put the fish fillets into a shallow pan with the stock, bay leaf and another knob of butter. Heat and simmer gently, partially covered, for 5 or 6 minutes, until the fish is cooked. The flesh will be opaque and should flake easily when tested with a fork. Use a draining spoon to lift the fish into the baking dish.
Pour the white wine into the pan with the fish cooking liquid. Remove the bay leaf. Add the blended cornflour and heat, stirring constantly, until thickened and smooth. Stir in the peas, courgettes and dill. Season, and then pour into the baking dish, gently combining it with the fish.
Drain the potatoes and mash them with the milk and any remaining butter. Season with a little salt and pepper to taste. Spoon on top of the fish mixture, spreading it out to cover the entire surface. If you prefer, pipe the potato on top of the fish. Transfer to the oven and bake for 25-30 minutes, until the potato topping is golden brown.
Cook’s tip: Place the fish pie under a hot grill for the final few minutes to make sure that the topping is well browned.
• 25g (1oz) butter
• 700g (1 ½ lb) potatoes, peeled
• 150g (6oz) courgettes, sliced
• 350g (12oz) wild Alaska halibut fillet, skinned
• 350g (12oz) wild Alaska salmon fillet, skinned
• 200ml (1/3 pt) vegetable stock
• 1 bay leaf
• 200ml (1/3 pt) dry white wine
• 2 tbsp cornflour, blended with 3 tbsp single cream or milk
• 75g (3oz) frozen petit pois or garden peas, thawed
• 1 tbsp dill, chopped
• 3-4 tbsp milk
• Salt and freshly ground black pepper