1. Base: Put the crushed biscuits in a bowl, add the melted butter or margarine and mix well. Press onto the base and up the sides of a pie dish with a 1,5 litre capacity. Refrigerate until ready to use.
2. Filling In a saucepan, heat 750ml (3c) of the milk, reserving the remaining cup to use later.
Add the butter or margarine and condensed milk and keep stirring with a whisk. Just as it starts to come to the boil, remove from the heat and set aside to cool slightly.