Step 1 Grease a 2.5cm deep, rectangle 11 x 35cm (base measurement) fluted tart tin with removable base. Reserve 5 Tim Tam biscuits. Process remaining Tim Tam until crushed.
Step 2 Add butter and process until combined. Press the mixture over the base and sides of the prepared tin. Place in the freezer for 15 mins to set.
Step 3 Meanwhile, for the milk chocolate ganache, combine the milk chocolate, cream, butter and sea salt in a microwave-safe bowl. Microwave on high, stirring every 30 seconds, for 1-2 mins, until melted and smooth.
Step 4 Set aside for 5 mins to cool. Pour over the tart base. Place in the fridge for 2 hrs, until set.
Step 5 Dark chocolate ganache – place dark chocolate and butter in a microwave safe bowl. Microwave on high for 1 min. Stir until melted and smooth. Set aside to cool slightly.
Step 6 Pour over the milk chocolate ganache and spread to the edges. Chill for 15-20 mins until set.
Step 7 Cut the remaining Tim Tam in half diagonally to make shards. Transfer tart to a serving plate. Top Tim Tam shards. Dust with cocoa.