Place the Milk and Vanilla Bean/Paste in a small pot and heat up on very low heat. Leave to infuse for about 5 minutes without boiling the milk (note 1)
In a seperate heat-proof bowl, whisk the Egg Yolks and Sugar until foamy. Add the Cornstarch (preferably sifted) and whisk until incorporated and smooth.
Carefully pour the warm milk over the Yolk/Sugar while continuously whisking (note 2). When all smooth, transfer the whole preparation back in the pot on low heat.
Keep whisking on low heat until the cream starts to thicken (note 3). When you see the first bubble (the cream starts to boil), keep whisking for 30 seconds then directly remove from the heat (note 4)
If adding the Butter, slice it into small cubes and add it to the warm, cooked cream away from the heat. Whisk well until fully incorporated and smooth.
Transfer the Pastry Cream into a large shallow pan or container (note 5) and cover with plastic wrap touching the surface of the cream (note 6).
Place in the fridge and leave to cool down set for at least an hour - or until cold.
Keep in the frigde for up to 3 days, until ready to be used. Before using, whisk the cream to loosen it.
If using Vanilla Bean, remove the bean from the pot, scrap the seeds with a small knife and put them back in the pot with the milk. Discard the pod or dry it out for another use.
This is to temper all the ingredients and make sure the eggs don't burn or curd once placed on the stove
Always work with low heat to avoid burning the cream and/or overcooking the eggs. It will take longer to thicken, but it is the best way to get the perfect creamy texture without any lumps.
The cooking time depends on the quantity of Milk. As a general rule, count 1 minute of cooking after the first boil for 1 litre of Milk. We are using half a litre of milk here, so we cook it for 30 seconds.
Storing the cream in a shallow pan or container will help the cream cool down much faster and more evenly as well.
It is important to cover the cream with wrap touching the surface to avoid the creation of a thin crust over the cream.