1
Boil the kettle. Heat the milk and cream in a saucepan or a microwave-safe bowl.
2
Combine the sugar and cornflour in a separate saucepan, then sift in the cocoa powder. Pour in 2 tablespoons of boiling water and whisk to a smooth paste.
3
Whisk in the egg yolks one at a time, then the warmed milk and cream, then the vanilla extract.
4
Scrape down the sides of the pan and set it over low heat. Cook, whisking, for 3-4 minutes until as thick as mayonnaise.
5
Remove from the heat and whisk in the finely chopped chocolate. Pour into four small cups or glasses, about 150ml/two-thirds of a cup each.
6
Cover the cups or glasses with cling film, touching the surface to stop a skin forming. Refrigerate once cooled. Don't serve them fridge-cold. Top with a dollop of cream, if you like.