Bring the milk to a gentle boil over a medium heat. Meanwhile, whisk the egg yolks with the sugar in a small bowl.

Add the flour and mix until completely smooth.

Add approximately 1/4 cup of warm milk to thin the mixture.

When the rest of the milk starts to boil, add it to the egg yolk mixture, stirring continuously.

Return it to the saucepan, and heat it over a high heat. Cook for around 1 minute until the creme patissiere thickens and boils, stirring constantly.

Lower the heat to medium and cook for around 2 minutes, continuing to whisk, until the cream loosens up.

Pour into a bowl and stir in vanilla.

Allow to cool, with plastic wrap directly on the surface of the creme patissiere to stop a skin forming.