Six 4cm deep ramekins with a base measurement of 7.5cm and a small solid baking tray
You will need to start the recipe at least on day before so the custards have time to freeze solid.
First of all heat the cream in a medium sized saucepan until it reaches boiling point, and while it’s heating blend the yolks, cornflour and caster sugar in a bowl. Then pour the hot cream in, stirring all the time with a wooden spoon, and return the mixture to the saucepan.
Heat very gently, still stirring, until the custard has thickened – which should only take a minute or two. (If it does overheat, don’t worry – if you remove it from the heat and continue to beat the custard it will become smooth again as soon as it cools.)
Now pour 350 ml of the custard into a glass heatproof jug and add the vanilla extract then stir the chopped chocolate into the remaining custard in the saucepan. Now divide the chocolate custard between the 6 ramekins and use the back of a spoon to smooth the surface than pour the vanilla custard on top.
Leave to cool, cover with cling film and chill for at least 3 hours then pre-heat your grill to its highest setting.
Uncover the ramekins and sprinkle each of the tops evenly with one tablespoon of granulated sugar.
Place them on a baking tray and put them under the hot grill for 4-5 minutes until the sugar has melted and started to go very dark brown in some places.
Leave to cool then cover with clingfilm and freeze overnight or until you need them.
Remove them from the freezer fifteen minutes before you serve them.