Add chocolate, condensed milk, butter, vanilla to slow cooker.
Cook on low for approx 90 minutes with the lid off stirring every 15 minutes with a metal spoon (I used a 1.5lt so cooking time will vary depending on your slow cooker)
Once ready, transfer into a bowl and stir through coconut, nuts, marshmallows.
Place into lined tin/container or silicone tray and set in the fridge.