Heat milk along with the vanilla bean in a sauce pan on a slow flame. When it comes to boil, remove from fire.
Over a double boiler, add sugar, flour, eggs and whisk it continuously until it gets thin without any chunks. Add the milk to it after removing the vanilla bean. Stir the mixture till thick. Remove from heat stirring continuously. Keep stirring to release the steam and prevent crusting. Cool mixture before serving.
Instead of Vanilla bean, you can also use few drops of vanilla essence.