Line a 20cm square cake tin with baking paper. Make sure you leave baking paper hanging over the sides to help you remove the slice once it has cooked. Preheat your oven to 180 degrees celsius.
Break the White Chocolate into squares and set aside until needed.
Place the self raising flour, brown sugar, cocoa, coconut and condensed milk into your Thermomix bowl and mix for 10 seconds, speed 4 REVERSE. Scrape down the sides of the bowl and add the white chocolate pieces and mix for a further 10 seconds, speed 4, REVERSE. If your mixture hasn't quite combined, mix for a further 5 seconds.
Pour the mixture into your prepared tin (don't worry, it will be VERY sticky!) and use two spoons to spread the mixture across the baking dish.
Place the slice into the oven and cook for 20 minutes. Allow the slice to cool completely before cutting into small pieces.