Split the vanilla pod in half lengthwise, and scrape the seeds out. Save the pod.
Separate the eggs, if necessary, making sure that the yollks do not break into the egg whites. Save the egg whites for later. Whisk 50g of caster sugar and the corn flour into the egg yolks. To prevent any clumps from forming, thin the yolks with a spoonful of milk.
Soak the gelatin sheets in ice cold water. Set aside.
Place the vanilla seeds and pod in a saucepan along with the rest of the milk. Bring up to a boil.
When the milk comes up to a boil, gently pour over the egg yolks while whisking.
Return the custard mix to the pan, and cook out over a medium heat. When the custard has thickened, pour into a bowl. Drain the gelatin sheets, and squeeze out any excess water before adding to the piping hot custard. Stir to combine and to dissolve the gelatin. Cover with a sheet of cling film, and leave to cool down to room temperature.
In a saucepan, combine 125g of caster sugar with 50ml of water, and bring to a simmer over a medium-high heat. The sugar syrup needs to reach 121'C.
Meanwhile, in a mixing bowl, vigorously whisk the egg whites so that they become very frothy. If you are using a stand mixer, turn down the mixer to a low speed until the syrup is ready. Otherwise, stop the mixer while you check on the sugar syrup.
When the sugar syrup reaches 121'C, start whisking the egg whites on a high speed, and carefully pour the hot syrup down the side of the mixing bowl. Continue whisking the egg whites until they cool down to room temperature. The meringue should be quite stiff and glossy when it is done.
Whisk the creme patissiere to loosen it. Whisk in a third of the Italian meringue to further soften the creme patissiere.
Pour the creme patissiere into the remaining Italian meringue, and fold gently until fully combined.
The Creme Chiboust is ready to be used. Chill the filled cake before serving.
«If you want a vegetarian version of Creme Chiboust, the gelatin can be left out altogether.»