Preheat oven to 200 degree C. Roll out shortcrust pastry and line pie mould with it. Remove the crust off. Pop it in oven and bake for 15 to 18 mins till the pastry is cooked and light golden.
Now Remove it and cool completely.
Take sugar, cocoa, cornflour in a sauce pan and mix well.
Add in milk and whisk well.
Now heat it and cook till it thickens.
Now take it off the heat and add in chopped chocolate and butter.