Preheat the oven to 350°F (175°C) and line a 9x13-inch baking dish with parchment paper.
In a large bowl, cream together butter and sugar for the shortbread base. Add flour and mix until combined. Press into the prepared dish and bake for 15-20 minutes, or until golden. Let cool.
In a saucepan, make the caramel layer by melting butter and brown sugar over medium heat. Add condensed milk and boil, stirring constantly, until thickened. Stir in vanilla and pour over the cooled shortbread.
Sprinkle chocolate chips over the caramel. Spread the melted chocolate, then top with pecans. Press gently to set.
Cool at room temperature, then refrigerate for 1-2 hours. Slice and serve.