Add the milk to a saucepan with the lemon zest or vanilla pod. Heat gently until just reaching a simmer. Remove from the heat and allow to cool slightly.

Mix the egg yolks and sugar in a bowl and beat with an electric whisk for 5 minutes until light and fluffy.

Add a third of the milk to the egg mixture, mixing constantly until smooth. Sift the cornstarch directly into the bowl and whisk well so no lumps remain.

Pour the egg mixture back into the pan with the milk and put it on a low heat, whisk constantly to avoid burning. Cook for about 8-10 minutes, until the custard thickens.

Allow to cool completely and keep it in the refrigerator until ready to use.

Storage

The custard can be kept in the refrigerator, closed in a glass container, for a maximum of 3 days. Can be frozen for up to 1 month.

Tip

In the event of lumps forming, let the cream cool and blend it with a blender.