Preheat the oven to 350 degrees F. Line a 9×13 baking dish with foil or parchment and spray with nonstick spray.
To make the crust: In the bowl of your electric mixer, beat the butter, brown sugar, flour and salt together, starting on low speed and increasing to medium. The mixture will be in coarse crumbs and almost dough like. Press it evenly into the bottom of the greased pan. Bake for 30 to 35 minutes, until slightly browned. Let it cool for about 10 to 15 minutes.
To make the filling, whisk together the eggs, syrup and sugar until smooth. Whisk in the bourbon and vanilla extract. Use a spatula to fold in the chocolate and pecans. Pour the filling over top of the crust. Bake for 30 to 40 minutes, until the center is set. Mine took closer to 40 minutes. One removed from the oven, sprinkle with flaked sea salt.
Let cool completely before slicing in squares. I love these refrigerated and served cold. They also freeze well too!