Grease and line the base and sides of a 20cm X 28cm rectangular slice tin with baking paper.
Place the biscuits into the Thermomix bowl and crush on Speed 9, 10 seconds. Remove and set aside in a seperate bowl.
Place the condensed milk and butter into the Thermomix bowl (no need to clean it) and melt on 80 degrees, 3 minutes, Speed 2.
Add the crushed Peppermint Crisp bars and the crushed biscuits to the Thermomix bowl. Mix on Speed 4, 5 seconds. Scrape down the sides of the bowl and repeat until combined.
Press the mixture firmly into the prepared tin. Melt the chocolate and vegetable oil (or coconut oil) in a clean Thermomix bowl on 50 degrees, 3 minutes, Speed 2.
Spread the melted chocolate over the top of the slice and decorate with your favourite chopped peppermint chocolates and biscuits.
Place into the fridge for 2-3 hours before cutting into slices.