Split the vanilla bean in half lengthwise using a small knife and scrape the seeds into a medium-sized saucepan. Pour in the milk and drop the bean pod into the saucepan. Bring to a slow boil.
In a separate bowl, whisk the egg yolks, sugar, corn starch and custard powder until smooth and creamy. (This will take some good arm work.)
Pour half of the boiling hot milk into the egg mixture and whisk vigorously. Then add the egg mixture back into the saucepan with the remaining milk.
Take out the vanilla bean and begin to whisk over low hear until the mix thickens and starts to bubble. This will take about five minutes.
Once it has thicken, add the butter and continue to whisk until it melts into the cream.
Transfer the cream to bowl and cover the surface with plastic wrap. The wrap need to be touching the cream. This prevents a crust or skin from forming on the surface of the cream.
Allow to cool before adding it to the shell.