Line a large baking tray approximately 30cm x 40cm with baking parchment.
Chop White Chocolate and melt in a glass bowl over a pot of gently simmering water, making sure the bottom of the bowl does not touch the water. Pour melted chocolate onto prepared tray and repeat with milk and dark chocolate.
Marble the chocolate together using the back of a spoon, and spread to fill the tray. Sprinkle with chopped cookies and place in the fridge until set - approximately 30 minutes.
Once chocolate is fully set, break into shards and serve.