Place the Milk in a medium-size saucepan. If using a vanilla bean, slice it in half lengthwise, scrape the beans inside the vanilla pod and add them to the milk along with the remaining pod.

Turn on medium low heat and bring to a simmer. Once it starts to simmer, turn off the heat, cover with a lid and leave to infuse for at least 20 minutes. If using vanilla paste or extract, you do not need to infuse the milk first.

In the meantime, whisk the egg yolks and sugar in a large heatproof bowl until smooth. Add the cornstarch and whisk until no lumps remain. You should get a thick mixture.

Slowly pour the warm milk (see note 1) over the egg mixture while you continuously stir to "temper" the eggs (see note 2). Whisk well until fully combined then pour the whole mixture back into the saucepan.

Place the saucepan over low heat and cook for about 5 minutes or until the custard has thickened and reached 82℃ / 180℉. Make sure the cream does not start boiling and to continuously whisk while the cream is cooking so that it does not stick to the bottom of the pan.

Transfer into a large clean bowl or shallow pan (to cool it down more quickly). Cover with plastic wrap touching the surface of the cream. Refrigerate for at least 2 to 3 hours, preferably overnight.

Pour the cold heavy cream in a large bowl (if using a hand mixer) or the bowl of your stand mixer fitted with the whisk attachment. Start whipping the cream on medium speed, slowly increasing to medium-high spread until you reach stiff peaks (see note 3).

Take the chilled pastry cream out of the fridge. If chilled in a shallow pan, transfer into a large bowl. Using a whisk, beat it lightly to loosen it.

Add about ¼ of the whipped cream to the pastry cream and gently whisk until fully incorporated. Switch to a spatula and add the remaining whipped cream in two or three times, gently folding it into the custard until it has been completely incorporated and you get a light, fluffy mixture.

If not using straight away, keep stored in the fridge (with plastic wrap touching the surface of the cream) until ready to use. It will last for up to 3 days.