Apply the milk and vanilla pod to the boil over low heat. Take off the heat and let it cool down a little. Beat the egg yolks with the sugar and stir in the flour and corn starch. Remove the vanilla pod and stir the milk through the egg mix. Pour the custard back into the pan and bring to the boil over a low heat. Cook and stir continuously for 1 minute. Covered with plastic wrap let cool and beat for use.