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.
Notes
RECIPE NOTES & TIPS
use an 18cm X 28cm greased and lined baking tin
you can use any plain sweet biscuits (such as Arnotts Marie)
you can use any soft filled peppermint chocolate you like (Cadbury peppermint is the most common peppermint chocolate block here in Australia)
if preferred, you can substitute the white chocolate melts on top for milk or dark chocolate
use full fat (not skim) sweetened condensed milk as it sets firmer
chill the slice in the fridge for 3 hours or until set
store in an airtight container in the fridge for up to 1 week
freeze any leftovers for up to 3 months
allow any frozen pieces of slice to defrost in the fridge before consuming