1.whisk the egg yolks with caster sugar till pale and fluffy.
2.pour the chocolate into the mixture together with the rum and the double cream.
3.whisk the egg whites in another bowl till soft peaks form.
4.then add the egg white to the chocolate mixture in 2 or 3 batches; mix well.
5.divide the mixture equally into 4 custard pots; chill for at least 2 hours.
6.serve by itself or with whipped cream.