Preheat oven to fanbake 180°C.
In a large saucepan over low heat melt together butter, sugar and cocoa.
Take off the heat then add Weetbix, flour, coconut and baking powder. Mix together.
Pour into a lined tray and press down firmly.
Bake for 15 to 20 mins until the slice is cooked but feels soft to the touch in the centre.
Icing: Mix together icing sugar, cocoa and butter.
Add boiling water as needed to loosen mixture and whisk out any lumps.
Ice the slice while it is still warm then chop up once cooled and icing has set.
