Preheat the oven to 180C/160C Fan/Gas 5. Line an 8" square baking tin.
Make the Anzac biscuit layer: place the butter, golden syrup and brown sugar in a medium pan over a medium heat. Heat and stir until melted and combined. Turn off the heat, add in the flour, oats, baking soda and coconut. Mix to form a sticky paste/dough.
Spread this into the lined tin and bake 25 minutes. Make the caramel whilst this is cooling.
Combine all caramel ingredients in a medium saucepan and place over medium heat. Let everything melt/combine before cranking up the heat, bringing the mixture to a boil.
Keep stirring everything for at least 5 mins whilst boiling – it will be bubbly and may splash so keep an eye on it and be careful! After about 6/7 minutes, the mixture should be golden/just edging on light brown and thickening up (keep going if not, until you reach this stage). Remove from the heat once it reaches this stage and pour it over the shortbread. Chill for at least an hour, until set.
Once the caramel has set, make the chocolate layer. Do this by breaking up the chocolate into a small bowl and microwaving in 20 second intervals, stirring in between, to prevent it from burning.
Pour the chocolate over the caramel layer. Sprinkle over more coconut to decorate (optional), and let set in the fridge another hour before slicing. Slice with a hot knife for best results!