Step by step method

1. Reserve 125ml milk, and mix the remaining milk with the condensed milk and vanilla essence and heat until hot but not boiling.
2. Mix the 125ml milk with the cornflour, cocoa and the eggs and add to the warm milk mixture.
3. Gently heat, stirring all the time until it thickens (about 5 minutes), remove from the heat and add the Stork Bake margarine.
4. Line a greased pie dish with tennis biscuits then gently spoon the milk filling over biscuits while still hot.
5. Chill until set.