In a medium size pan bring the milk to the boil

In a large mixing bowl whisk the egg yolks, caster sugar and vanilla purée

Then whisk in the flour

Gradually add the hot milk and whisk continuously

Pour the mixture back into the pan and over a medium heat, bring to the boil.

Whisk constantly for about 1 minute, to achieve a smooth consistency

Remove from the heat and add the chocolate

Mix until completely incorporated

Immediately pour into a glass bowl and sprinkle caster sugar over the top to prevent a skin forming

Cool down and once cool cover with cling film and refrigerate until needed