Instructions
Begin by placing the floury potatoes in a large pan filled with cold salted water. Bring this to a gentle boil, then reduce the heat to a simmer, cover, and cook for 15 minutes until the potatoes are tender when pierced with a fork. Drain them thoroughly and return the potatoes to the pan placed over low heat for about 30 seconds; this step helps evaporate any excess moisture, ensuring a fluffy mash. Mash the potatoes with 1 tablespoon of olive oil and season with salt and pepper to taste. Set aside. While the potatoes cook, pour the semi-skimmed milk into a large sauté pan. Gently add the white fish fillets and bring the milk just to a boil. Immediately remove the pan from the heat, cover it, and allow the fish to poach gently in the hot milk for 3 minutes. Carefully remove the fish with a slotted spoon, reserving the cooking milk. Pat the fish dry with kitchen paper, flake it gently into an ovenproof dish, making sure to discard any skin and bones. Heat the remaining olive oil in a clean pan. Stir in the plain flour and cook for 30 seconds to form a roux. Gradually whisk in 200 to 250 ml of the reserved poaching milk, discarding the remainder. Grate a little nutmeg into the sauce and season it with salt and pepper. Let it bubble gently until it thickens to a creamy consistency, then stir in the double cream until fully combined. Preheat your oven to 190°C (fan 170°C, gas mark 5). Prepare your additional ingredients by grating the Jerusalem artichokes and slicing the leek finely. Add these to the flaked fish along with the peeled raw prawns and a generous handful of chopped parsley and dill. Stir in the grated lemon zest and juice into the creamy sauce before pouring it over the fish and vegetables. Using a wooden spoon, gently mix everything together to combine. Spoon the mashed potato over the fish mixture, spreading it evenly. Use a fork to create textured peaks on the mash – these will brown beautifully in the oven, adding a delightful crispiness. Sprinkle the grated Gruyère cheese evenly over the top. Place the dish in the oven and bake for 35 to 40 minutes until the top is golden and bubbling. The cheese and potato will form a luscious crust, while the filling remains wonderfully creamy beneath. Serve the pie hot, accompanied by simply wilted greens for a balanced and satisfying meal. Tips: To save time, you can prepare the mashed potatoes and fish mixture in advance and assemble just before baking. Be sure not to overcook the fish in the milk – it should be tender but still hold together when flaked. For extra richness, feel free to add a knob of butter to the mash or sprinkle extra cheese over the top before baking.
