Grease and line two 20cm round springform baking pans.
In a medium saucepan over low heat, add butter, white chocolate, caster sugar & milk. Stir continuously until mixture is fully combined and smooth. Remove from heat and allow to cool for a few minutes.
In a large bowl add plain flour and self-raising flour.
Add white chocolate mixture, eggs & vanilla extract. Using a wooden spoon or spatula, stir until fully combined.
Pour mixture evenly into the two baking pans.
Place in oven and cook for 45-50 minutes or until a skewer inserted into the centre of the cake comes out clean. Remove from oven and allow to cool for about 10 minutes before turning out onto wire racks to cool completely.
Ganache
Add white chocolate bits and thickened cream to a large heatproof bowl.
Place over a saucepan of simmering water and stir mixture until fully combined and smooth. Remove from heat, allow to cool then chill in the refrigerator for about 60 minutes until mixture has thickened.
Remove from refrigerator and whisk for about 30 seconds.
Divide mixture evenly between 2 bowls.
Crush half the Oreos, add to one bowl and fold through the ganache.
Cake Assembly
Place one cake onto a plate and top with the Oreo ganache.
Place the second cake upside down on top of the ganache. Note. level the cake by trimming the top if required.
Top this cake with the white chocolate ganache.
Break the remaining Oreos and place on top of the cake.
Add cookies and cream chocolate on top of the ganache if required.