For the Fudge Topping:
In a microwave-safe bowl, combine the chopped chocolate, sweetened condensed milk and butter. Microwave, uncovered, on low, in 30 second increments, stirring in between each increment, until the chocolate is completely melted; stir mixture smooth. Stir in vanilla extract. Spread mixture over the shortbread, smoothing with a spatula into an even layer. Pour salted caramel on top of the chocolate mixture, then sprinkle with the toasted pecans. Refrigerate until firm; about 2 hours. Cut into small squares and serve.