Place a piece of baking paper on a large baking tray and set to one side. Toast the coconut flakes in a dry pan until golden. Set aside to cool.
Chop the pistachios very roughly (I like to keep a few of them whole). Set aside.
Melt the dark, white and milk chocolate – see cook’s notes above. Mix half of the pistachios into the dark chocolate. Pour the dark chocolate onto the lined baking tray and spread into a rough rectangle about 16cm x 24cm. It doesn’t need to be exact.
Spoon teaspoonfuls of white and milk chocolate on top of the dark chocolate. Use a large skewer or chopstick to swirl the chocolates together.
Sprinkle the coconut and remaining pistachios over the chocolate. Leave to cool and set. Once set cut or break the bark into pieces. Store in an airtight container in a cool place.