Line an 18X28cm slice tin with baking paper - make sure you leave paper hanging over the sides.
Place the biscuits into your Thermomix bowl and mix for 6 seconds, Speed 8 to crush. Transfer to a separate bowl and set aside until needed.
Without washing the Thermomix bowl, add the butter (cut into cubes), sweetened condensed milk and peppermint chocolate and cook for 3 minutes, 60 degrees, Speed 3 or until melted.
Add the biscuits to your Thermomix bowl and mix for 20 seconds, Speed 2 REVERSE or until combined.
Pour the mixture into your prepared tin (it will be a little sticky) and use a metal spoon to spread and flatten the surface.
Place the white chocolate melts into a CLEAN Thermomix bowl and cook for 3 minutes, 50 degrees, Speed 2 before scraping down the sides and cooking for a further 1 minutes, 50 degrees, Speed 2 or until melted.
Pour the melted white chocolate over the top of your slice and place it into the fridge for 6 hours (preferably overnight) to set before cutting into small pieces.