Line an 18 x 28cm slice tin with baking paper and set aside.
Place butter into Thermomix bowl and melt 3-4 min/60°C/speed 2.
Add biscuits and select the Turbo function. Blitz 2 sec/2 – 3 times or until the biscuits are combined.
Add the cocoa, vanilla, salt flakes, coconut and sweetened condensed milk to the Thermomix bowl and blend 12 sec/speed 5/reverse. Use your spatula to help push the mixture down into the blades. Combine a further 10 sec/speed 5.
Press mixture into your prepared slice tin.
Place the white chocolate in pieces with the coconut oil into ziploc bag. Follow the instructions for melting small amounts of chocolate in that recipe.
Pour the melted chocolate over your chocolate slice, spread evenly using a palate knife, then decorate with the M&M's and sprinkles as you wish. (Gold leaf is also a bit fun!)
Place the slice into the fridge for a minimum of 2 hours to firm before cutting into pieces. Wrap and gift or just serve as you wish.