Grease and line a rectangular (32X20cm) baking tin with baking paper.
Finely crush biscuits in the TM bowl on Speed 8 for 10 seconds. Scrape down the sides and repeat for another 10 seconds. Set aside.
Place the butter and peanut butter into the TM bowl and melt on 100 degrees, Speed 1 for 3 minutes.
Add the icing sugar and crushed biscuits and mix on Speed 2 for 30 seconds.
Spread the mixture evenly into the baking tin and set aside.
Place the white chocolate and extra peanut butter into the TM bowl and melt on 80 degrees, Speed 1 for 2-3 minutes (you may need to scrape down the sides of the bowl occasionally).
Pour over the top of the slice.
Place into the fridge for 3-4 hours before removing and cutting into pieces.