Place two sheets of gelatine in a bowl of cold water and allow to soak for about 10 minutes
Whisk together 4 egg yolks, 50g (2oz) caster sugar and 2 tablespoon cornflour until blended.
Heat 250ml (9floz) milk until it just comes to the boil, then slowly beat into the egg yolk mixture. Return to the pan and cook over a low heat whisking constantly until thickened.
Pour the thickened custard into a bowl. Stir in the vanilla paste. Remove the gelatine from the water and squeeze out the excess water. Add to the hot custard and whisk together until the gelatine has dissolved. Cover with a sheet of dampened parchment paper and allow to cool.
Meanwhile, place 125g (4oz) caster sugar in a saucepan with 4 tablespoon water. Heat gently stirring until the sugar has dissolved then increase the heat and heat until the syrup reaches to 121°C (250 °F).
While the sugar syrup is coming to temperature, whisk egg whites until very frothy.
As soon as the sugar syrup reached the correct temperature, carefully pour the hot syrup in a steady stream down the side of the mixing bowl, while whisking on high speed. Once all the syrup has been added, continue whisking the egg whites until they cool down to room temperature and you have a very stiff and glossy meringue.
Stir the cooled crème patisserie to loosen slightly then mix in about one-third of the meringue. Then add the crème patisserie mixture to the remaining meringue and mix in.
The creme chiboust is ready to use.