Preheat oven to 180°C. Put aluminium foil in a shallow 29cm x 21cm slice dish.
Base: Sift flours into a bowl, add coconut. Combine brown sugar and butter in a pan until sugar has dissolved. Add mixture to the flours and stir. Press into tin with back of spoon, bake for 10 mins or until brown.
Filling: Combine butter, Golden Syrup and condensed milk in a saucepan. Stir for 5 to 10 mins until mixture boils and browns (watch it doesn't burn on bottom). Smooth over the base and bake for 15-20 minutes until just starting to caramelise around the edges.
Topping: Combine chocolate and butter in a heatproof bowl, stand over pan of boiling water until melted. Allow the filling to cool before spreading over the chocolate topping.