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-sized 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.

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, stirring continuously, to make base of sauce.

Add 1/2 the 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 the 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.