Combine butter, sugar and flour for base in a stand mixer and mix until crumbly (you can also do this with a pastry cutter or your hands). Press into the bottom of a 10x15" pan (you could use a 9x13", but you will have thicker bars).
Bake 12 minutes or until slightly golden. Remove from oven, sprinkle with ½ cup coconut, and let cool while you prepare the filling.
Combine sugar, corn syrup, butter, and sweetened condensed milk in a large pot. Heat over medium heat until it comes to a boil, watching carefully and stirring often.
Boil 5 minutes, stirring constantly. Add coconut extract. Pour over the coconut on the crust. Let cool completely before add the chocolate.
In the same pot, melt the chocolate and butter slowly over low heat, stirring often. Spread over the caramel layer and sprinkle immediately with the rest of the toasted coconut, pressing it lightly into the chocolate.