Pour cocoa, milo and boiling water in a saucepan and stir. On low heat add butter, sugar, vanilla, eggs and condensed milk then stir until mixture thickens. It will take about 15 minutes of stirring to get a custard-like consistency.
Break biscuits into quarters and stir into the custard mixture.
Prepare a container, I use 15x15cm square container. You can line the container with baking paper for easy removal.
Pour the mixture into the container and smooth out. Refrigerate for about 3-5 hours but I like to keep it overnight so that the custard sets properly.