Line a 20cm square tin with non-stick parchment paper. 

Add the condensed milk and white chocolate to a saucepan over a low to medium heat. Stir until the mixture has melted. 

Allow to cool slightly, then fold in half the cookies, half the milk, half the white and half the dark chocolate chips. 

Pour into a prepared tin and smooth the top with a spatula. Sprinkle the remaining chocolate chips and the crushed cookies over the top. 

Refrigerate for a minimum of 4 hours or overnight. 

Use a knife to cut into around 12 squares and serve.