Preheat oven to 180 degrees (fan forced). Grease and line an 18X28cm rectangular slice tin with baking paper.
Place the butter into the Thermomix bowl and melt for 2 minutes, 80 degrees, Speed 2.
Add the plain flour, self raising flour, coconut and caster sugar and mix for 15 seconds, Speed 4.
Scrape down the sides of the bowl and mix for a further 20 seconds, Speed 4. Note: the mixture will be very crumbly.
Press the mixture into the prepared tin and press down firmly.
Bake for 10 minutes and then remove from the oven.
Sprinkle over the white chocolate chips and the nuts.
Pour the can of sweetened condensed milk over the top of the nuts (ensuring all parts are covered).
Bake for a further 20-25 minutes or until golden.
Set aside to cool before placing into the fridge for 3-4 hours (preferably overnight). Cut into slices to serve.