You will need to make the custard base and caramel simultaneously so both are ready at the same time. Heat the cream and milk in a small heavy-based saucepan over low heat to simmering point.
Using an electric mixer, whisk the egg yolks and 90 g of the caster sugar in a heatproof bowl for 5 minutes or until pale and creamy. Slowly add the hot milk mixture, then wh