Step 1 Place chocolate and butter in a heatproof, microwave safe bowl. Microwave on medium, for 1-2 minutes, stirring in between until smooth. Set aside for 2 minutes. Stir in egg yolks.
Step 2 Place cream in a bowl, using an electric mixer, beat until soft peaks form.
Step 3 Beat egg whites in a bowl until soft peaks form. Then, gently fold cream into chocolate mixture. Stir in 2 tablespoons of the egg white. Fold in remaining egg white.
Step 4 Finely chop 6 Tim Tam biscuits and fold into mousse. Spoon mousse into glasses. Refrigerate for 3 hours or until firm. Chop remaining Tim Tam. Blueberries and whipped cream to serve.