First you have to make the crust. You will need a 9x13 pan. You do not have to grease the pan. Put two cups of all purpose flour in a bowl. Next, mix in four tablespoons of brown sugar. Stir the brown sugar and flour together, then cut in one cup of butter cut in to pieces. Mix it into the mixture until the mixture is coarse using a pastry blender, then pour the crust into the 9x13 pan and spread it out evenly in the pan and then firmly press it down into the pan. Put it into an oven preheated to 350 degrees for twenty minutes, then take a pot and put one can of sweetened condensed milk into it. Do not use evaporated milk. Next you will add one cup of brown sugar and four tablespoons of white corn syrup, then you will add one cup of butter (two sticks). The mixture should be brought to a boil and cooked over medium heat for five minutes. Make sure that you stir the mixture constantly while it cooks for the five minutes. Take the crust out of the oven and pour the hot caramel mixture into the crust. Spread the caramel out over the crust and let it cool for a few minutes. After it has cooled put it in the refrigerator until the caramel is completely set. For the final step you need to melt three chocolate bars. Take them out of the wrapper and put them in a measuring cup. Put the measuring cup in the microwave and melt the chocolate. Pour the melted chocolate over the caramel crust in the pan. Spread the chocolate out over the caramel until it completely covered and smoothed out. Put it back in the refrigerator to cool. After it is all set, take it out and let set until it comes to room temperature then cut it into squares. Once you've cut it the shortbread bars are ready to eat.