Line a 7" flan tin with the pastry and bake blind.
Mix cocoa and cornflour to a paste with a little of the milk.
Bring the remainder of the milk to the boil with the sugar, pour on the paste, then return to the saucepan and bring to the boil again, stirring all the time.
Cook for 2 minutes, then pour into cooked flan case and leave to cool.
Decorate with piped cream.