Preheat oven to 200°C or 180°C fan. Grease six 1-cup capacity ramekins. Place on a baking tray.
Melt butter in a saucepan on low heat. Stir in flour and cook for 1 minute. Remove from heat and mix in milk. Return to medium heat, stirring, until sauce boils.
Stir in chocolate and vanilla extract. Remove from heat and cool slightly. Beat in egg yolks one at a time. Transfer to a large bowl and set aside to cool.
Using an electric beater, beat eggwhites in a large bowl until soft peaks form. Gradually beat in caster sugar until firm peaks form. Fold into chocolate mixture. Spoon mixture into prepared ramekins. Bake for 15-20 minutes, until souffles rise. Dust with icing sugar and serve with cream.