Golden-Topped Fish Pie with Leeks and Peas

Preheat the oven to 175 °C (350 °F).

In a large pot, add the diced potatoes and cover with salted water. Bring to a boil, then reduce heat to medium-low and simmer until tender, around 20 minutes. Drain and let cool.

In a large pan, combine milk, bay leaf, and nutmeg. Gently simmer over medium-low heat. Add cod and poach until flaky, about 5 minutes. With a slotted spoon, transfer the cod to a plate; reserve the poaching liquid.

Mash the potatoes in a large bowl. Mix in 3 tablespoons of butter and 2 tablespoons of the reserved poaching liquid until the potatoes are stiff but not runny.

In a skillet, heat 1 tablespoon of butter over medium heat. Add the chopped leek and cook, stirring often, until softened and translucent, about 5 minutes. Set aside.

In the same large pan used for poaching the cod, melt the remaining 1/4 cup of butter over medium heat until it just stops bubbling. Add flour and stir the roux continuously for 1 minute. Gradually pour in the remaining poaching liquid, continuously stirring, to create the sauce base. Add half of the grated Cheddar cheese and stir until melted. Incorporate the flaked cod, leek, peas, and season with salt and pepper.

In an oven-safe dish, place the fish mixture. Gently position the hard-boiled eggs on top of the filling. Cover with a generous layer of mashed potatoes. Sprinkle the remaining Cheddar cheese over the potatoes.

Bake in the preheated oven until the top is starting to brown, approximately 30 minutes. Serve immediately.