Put a little sugar in a saucepan and pour the milk over it, then scrape out the seeds from the vanilla pod and add them and the bark to the milk. Adding a little sugar at the start will prevent the cream from sticking to the bottom of the saucepan.

Bring to heat and warm it up a bit without boiling. Remove from the heat, cover with plastic wrap, and let it infuse for at least 30 minutes.

Whisk the egg yolks with the sugar until pale. You can use a magic or a regular whisk.

Sift in the cornstarch and flour. whisk to smooth and combine. Do not overwhisk.

Bring the milk to the boil. Remove just before boiling, and pour a little over the egg mixture through a sieve. Mix well to blend the egg mixture with the milk.

Add the remaining milk, stir and transfer to the saucepan.

Bring to a boil over medium heat, stirring constantly. The cream will thicken gradually. Do not stop cooking just after it has thickened, wait another minute. Remove the pastry cream from heat when it starts to form air bubbles. Stop whisking occasionally to check its progress.

Boil the cream for 1 min 30 to pasteurize it and prevent bacteria from developing.

Off the heat, add the butter and stir to incorporate.

Pour the custard into a large dish to cool quickly. Cover it with plastic wrap directly on the surface to prevent it from forming a skin on top.

You can prepare it the day before for the next day. You will just need to whisk it to loosen and smooth it before using it in other creams or to fill cakes.