Line a 28 x 18 cm slice tin with baking paper, making sure that you leave plenty hanging over the sides to help your remove the slice once it has set.
Place the biscuits into your Thermomix bowl and use the 1 sec Turbo function to crush until they are broken up into approximately 2 – 3cm pieces. Transfer to a separate bowl and set aside until needed.
Break the Peppermint Crisp Bars in half and place into your Thermomix bowl, blitz for 2 seconds, speed 4 to break into small pieces. Set aside in a separate bowl until needed.
Without washing the Thermomix bowl, add the butter (cut into cubes), condensed milk and peppermint chocolate which has been broken into squares and cook for 3 minutes, 60 degrees, speed 3. If it’s not quite combined at the end of the cooking time (time taken will depend on temperature of the ingredients), cook for a further 1 minute, 60 degrees, speed 3.
Add the biscuits and HALF of your peppermint crisp pieces 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 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 use the remaining peppermint crisp pieces to decorate it. Place it into the fridge for a minimum of 2 hours to set before cutting into small pieces.