Preheat oven to 350 degrees F. Butter the bottom and sides of a 8 inch metal baking pan. Put a long piece of parchment paper in the bottom of the pan, letting the parchment extend up two sides of the pan and overhang slightly on both ends. (This will make it easy to remove the bark from the pan once set); set aside.
Toast the coconut by spreading onto a rimmed baking sheet. Toast stirring frequently, until the coconut is an even golden brown color, about 6 to 8 minutes. Set coconut aside to cool. Reserve 2 tablespoons for topping.
In a small saucepan over high heat, bring the sugar and water to a boil swirling the pan gently, until the sugar has dissolved (Do not stir) Cook, gently swirling the pan occasionally, until it has the color of straw. Turn the heat down to medium and continue to cook, gently swirling the pan occasionally, until the caramel turns a medium amber color. Add the butter and heavy cream to saucepan and whisk to combine. Set aside to cool completely. Reserve 2 tablespoons of the caramel for topping.
In a metal bowl set over a pan of lightly simmering water, melt chocolate, stirring occasionally until smooth, and remove from heat. Reserve 2 tablespoons for topping.
Pour half of chocolate into prepared pan, use an offset icing spatula to smooth the chocolate into an even layer. Sprinkle coarsely crushed shortbread on top and gently press it into the chocolate. Transfer pan to the freezer for 5 minutes or until chocolate becomes slightly hardened.
Fold the toasted coconut into the caramel sauce. Remove the pan from freezer and pour caramel/coconut sauce on top. Use an offset icing spatula to smooth it into an even layer. Transfer pan to the freezer for 5 minutes or until caramel becomes slightly hardened.
Remove pan from freezer and pour other half of chocolate on the caramel/coconut layer. Use an offset icing spatula to smooth the chocolate into an even layer. Immediately sprinkle with reserved coconut and gently press to adhere. Drizzle remaining 2 tablespoons of chocolate and caramel on top of the coconut. Transfer pan to refrigerator for about 5-10 or until bark is set. Keep refrigerated until ready to serve.