Peel and quarter onion, stud each quarter with a clove.

Pour the milk into a large saucepan, crumble fish stock cube into the milk and stir over a low heat to dissolve.

Add the bay leaves, onions, and fish fillets. Bring up the heat until the milk is bubbling gently, then poach the fish at a low simmer for 8 minutes.

Meanwhile, boil the eggs and set aside to cool.

Peel and cut the potatoes into cubes and boil until soft.

Add the mustard powder and nutmeg to the flour.

Layer the seafood mix in the bottom of a casserole dish.

Remove poached fish from milk broth with a slotted spoon and layer over the seafood mix.

Next, remove the onions from the broth and put aside. Discard cloves and bay leaves.

Peel the eggs and slice using an egg slicer. Layer over the fish in the casserole dish, then layer the onions over the eggs. Season to taste with parsley.

Melt the butter in a pan. Gradually add the flour mixture and 500ml of the milk broth. Whisk together well until thickened.

Pour sauce over the fish, egg, and onion layers, shaking the casserole dish gently to ensure the sauce settles to the bottom of the dish.

Mash the potatoes together with the remaining 100ml of milk broth. Layer the mash evenly over the top of the pie.

Grate cheese over the potato, and bake at Gas Mark 6 for 40 minutes.