Toast the coconut with the mac-nuts and set aside to cool. Mix the coconut milk, corn syrup, and salt together and set aside. In a pan combine the sugar and water. Heat the pan over high heat. Stir until the sugar has dissolved. Do not stir after the mixture begins to boil. Boil until the syrup reaches 310 degrees. Remove from heat and cool for 1 minute. Add the coconut milk mixture to the syrup and return to the heat. Stir until the sugar dissolves into the milk and cook until the caramel reaches 240 degrees. Remove from heat and stir in the coconut. Pour the caramel over the shortbread. Allow to cool to room temperature and refrigerate for 30 minutes.