Put 400g of skinless white fish fillets and 400g of skinless smoked haddock fillets in a large pan with 500ml of whole milk, 1 small quartered onion studded with 4 whole cloves, and 2 bay leaves. Simmer for 8 minutes.
Lift out the fish and flake it into a baking dish. Strain the milk and let it cool.
Meanwhile, cook 4 eggs in simmering water for 8 minutes. Cool, peel, and quarter them, then arrange over the fish with 1 bunch of chopped parsley.
Melt half of 100g of butter and stir in 50g of all-purpose flour. Gradually whisk in the cooled milk and cook until thickened. Season with salt, pepper, and a little grated nutmeg, then pour over the fish.
Preheat the oven to 400°F / 200°C. Boil 1kg of peeled starchy potatoes, cut into chunks, until tender. Drain and mash with the remaining butter and 100ml of whole milk.
Spread the mash over the filling and bake for 30 minutes.
