Place the fish, peppercorns and sliced leeks in a pan and cover with water.

Bring the boil and then simmer for 5 minutes or until fish is cooked through (if using frozen fish simmer for 10 minutes).

Skim away any scum from the surface.

Drain the fish mixture over a bowl, removing the peppercorns and reserving the fish stock.

To make the sauce put 200 mls fish stock, milk, butter, cream (if using) and flour in a pan and bring to a simmer whisking constantly until thickened.

Add the mustard and grated cheese and mix well until melted.

Then add the fish, cornichons and sweetcorn.

Unroll the pastry sheet and using an upturned deep pie dish as a template cut around it with a knife to form the pie lid.

Pre-heat the oven to 200°C.

Cut 3 narrow strips from the edge of the remaining pastry and use these to cover the rim of the pie dish, breaking off any excess (wet the base with a pastry brush).

Brush the outer rim of the pastry lid with water and place on top of the pie.

Cut out fish shapes etc brushing with water to adhere to the pie.

Pierce a whole with a knife under one of the fish for ventilation.

Crimp the edges together by putting your left hand index finger and thumb on top of the edge pulling the pastry upwards with your right hand index finger going along the whole rim until finished.

Brush the egg wash over the pie.

Place pie in the oven and bake for 20 minutes until golden and cooked through.

Serve with vegetables of your choice.