Shortbread

1. Preheat the oven to 350°F. Line a 9×9 baking dish with foil and coat with nonstick spray. Set aside.
2. In the bowl of your stand mixer fitted with the paddle attachment mix the butter, sugar, and salt together on medium speed for 1 minute. Add in the flour and mix on low speed until just combined. Press the dough evenly into the bottom of the prepared pan and bake for 15-20, or until lightly golden at the edges.
3. Remove from oven and set aside.

Caramel Filling

1. In a medium saucepan combine the butter, brown sugar, corn syrup, and condensed milk. Bring mixture to a boil and continue to boil for 5 minutes, stirring frequently. Remove from heat and using a wooden spoon, stir vigorously for 3 minutes to cool and aerate.
2. Pour the caramel over the (cooled or warm) crust and spread evenly to the edges. Cool completely.

Topping

1. In a microwave-safe bowl, melt the chocolate in 30 second increments, stirring in between, until completely melted and smooth. Pour the chocolate on top and spread evenly to the edges using an offset spatula. Sprinkle with flaked sea salt, if desired.
2. Allow the chocolate to set completely and then cut into squares.