Traditional British Fish Pie

Preheat the oven to 350 degrees F (175 degrees C).

Place potatoes into a large pot and cover with salted water; bring to a boil. Reduce heat to medium-low and simmer until tender, about 20 minutes. Drain and let cool.

Combine milk, bay leaf, and nutmeg in a large pan and bring to a gentle simmer over medium-low heat. Add cod and poach until flaky, about 5 minutes. Use a slotted spoon to transfer cod onto a plate; reserve poaching liquid. Use a fork to flake fish into bite-size pieces.

Mash potatoes in a large bowl. Mix in 3 tablespoons butter and 2 tablespoons poaching liquid until potatoes are fairly stiff and not too runny.

Heat 1 tablespoon butter in a skillet over medium heat and stir in leek. Cook and stir until softened and translucent, about 5 minutes. Set aside.

Melt remaining 1/4-cup butter over medium heat in a large, deep skillet until it just stops bubbling. Add flour and stir roux continuously for 1 minute. Slowly pour in remaining poaching liquid, continuously stirring, to make base of sauce. Add 1/2 of sharp Cheddar cheese and stir until melted. Fold in flaked cod, leek, and peas. Season with salt and pepper.

Place fish mixture in an oven-proof dish; press boiled eggs gently into filling across the surface. Cover with a thick layer of mashed potatoes. Sprinkle with remaining Cheddar cheese.

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