Grease and line 21cm (internal) round springform cake tin with baking paper. Both sides and bottom.
Line sides of tin with Tim Tams. You need to do this first to determine how many Tim Tams you need for the side of the cake and how many are left over for the base. You should use about 16 Tim Tams. Once this is done remove Tim Tams and put aside.
Crush remaining Tim Tams in food processor.
Add butter until combined.
Remove from processor and press mixture evenly over base of cake tin.
Replace Tim Tams around outside edge of base and put in refrigerator.
Cream Cheese Filling
Melt white chocolate in a bowl over a saucepan with heated water. Set aside to cool.
Melt dark chocolate in a separate bowl over a saucepan with heated water. Set aside to cool.
With an electric mixer, beat cream cheese and caster sugar in a separate large bowl until light and fluffy.
Add cooled melted white chocolate and continue beating until combined.
Fold in cream until just combined.
Transfer 1/3 of mixture to a separate bowl and fold in dark chocolate until just combined.
Spread white and dark mixtures alternately over base in cake tin.
Smooth over top, cover and refrigerate overnight before serving
Decorate with sifted cocoa powder and sprinkle top with broken pieces of flake choclate bar to serve