Grease and line a 22 X 28cm rectangular slice tin with baking paper and set aside.
Place the butter into the Thermomix bowl and melt on 80 degrees, Speed 2, 2 minutes (or until melted).
Add the chocolate biscuits and Oreo cookies to the Thermomix bowl and blitz on Speed 8, 5 seconds. Scrape down the sides of the bowl and repeat for a further 5 seconds.
Add the condensed milk and mix on Reverse, Speed 4, 15 seconds, or until well combined. If the mixture is too crumbly, add a little more condensed milk and mix on Reverse, Speed 4, 10 seconds.
Press the mixture firmly into the prepared tin and place into the fridge.
Break the Cookies & Cream chocolate into pieces and place into a clean and dry Thermomix bowl. Add the coconut oil and melt on 50 degrees, Speed 2, 3-4 minutes (or until melted and smooth).
Pour the melted chocolate over the chocolate base and place back into the fridge for 3-4 hours to set.
Cut into slices using a hot knife and store for up to 1 week in an airtight container in the fridge.