Grease and line an 18cm X 28cm rectangular slice tray with baking paper and set aside.
Place the biscuits into the Thermomix bowl and roughly chop by pressing Turbo 5-10 times. Remove and set aside.
Place the condensed milk, butter and peppermint chocolate into a clean Thermomix bowl. Melt on 80 degrees, 3 minutes, Speed 2.
Add the cocoa powder and peppermint essence and mix on Speed 5, 10 seconds. Scrape down the sides of the bowl.
Add the crushed biscuits and mix on Reverse Speed 3 (using the spatula to assist) until combined.
Spread the mixture into the prepared baking tray.
Melt the chocolate in a clean Thermomix bowl on 50 degrees, 3 minutes, Speed 2.
Pour the melted chocolate over the top of the slice, decorate with the chopped candy canes and M&Ms and place into the fridge for a minimum of 3-4 hours.
Allow the slice to come to room temperature before cutting into pieces.
Store in an airtight container at room temperature (or in the fridge) for up to 5 days.