Place milk, butter, onion, parsley into a saucepan and slowly bring to boil turn down to a simmer.
Add fish and seasonings simmer for a few minutes
Thicken with cornflour mixed with milk and set aside to cool.
Roll out pastry to fit a 25cm dish bringing the pastry up the sides. add fish mixture when it has cooled and decorate the top in a cross pattern with pastry strips and filling in the open areas with the potato pompoms.