Lightly grease an 6 inch loose base cake tin. (I also added a greaseproof paper circle at the bottom to help it off the base later).
Melt the butter gently in the microwave in short bursts or in a pan and then take off the heat so it doesn't burn.
Crush the shortbread biscuits in a food processor, or put it in a plastic bag and use a rolling pin to break them up (my preferred method to leave them as a larger crumb).
Put the biscuit crumbs in a bowl and add the melted butter. Stir until all the biscuits are coated in the butter.
Scoop the crumbs into the tin and push down gently to make a hard layer. Place the cake tin in the fridge and leave to harden for 30 minutes while you make the cream layer.
In a bowl cream together the cream cheese and caster sugar until the sugar has dissolved and is well distributed.
Stir in the double cream and cream cheese mixture together.
Take 120g of the Toberlone and chop up into small chunks. Stir in to the cream mix
Remove the cake tin from the fridge and add the cream cheese to the base and put back into the fridge to set for at least an hour. Longer is fine if you want to make it ahead of time for an event.
Remove the cheesecake from the tin and place on a plate.
Melt the milk chocolate and allow to cook slightly before drizzling over the cheesecake.
Whisk the remaining double cream until it starts to thicken. Add a star nozzle to a pipping bag and add the cream. Pipe the cream into swirls on to the cheesecake.
Lightly chop up the remaining Toberlone and add it to the centre of the cheesecake.
Serve and enjoy.