Preheat the oven to 350ºF. Line a 9×9 pan with parchment paper or spray with non-stick cooking spray. Set aside.
Combine the flour and sugar in a medium-sized bowl. Then cut the butter in with a pastry cutter or two forks, until it forms a crumb mixture. Then press down into the pan and bake for 20 minutes. Remove from oven and allow to cool.
For the caramel, add the butter, brown sugar, corn syrup, and sweetened condensed milk to a medium saucepan and melt over medium heat. Bring to a boil and cook for 4-5 minutes, stirring constantly, if you do not stir it constantly it will burn and harden quickly. Remove from heat and stir an additional 2 minutes, or until it starts to thicken. Pour over cooled shortbread bars. Allow to cool.
Once the caramel has become firm, mix the chocolate and oil in a microwave-safe bowl. Cook on high for 1 minute. Stir and cook in 15-second intervals, until the chocolate is melted. Then pour over the caramel layer and allow to set. Place in the fridge to help set faster.
Once the chocolate has hardened, cut into squares.
