Preheat oven to 350 degrees. Butter a pie plate very liberally.
For the Crust: In a food processor, process the shortbread cookies and the flour until well combined. Add in the salt and butter and pulse until the mixture resembles fine crumbs. Pour the crumb mixture into the buttered pie plate. With the back of a 1 cup measuring cup, press the pie crust into shape and up the sides of the dish. CHILL for 30 minutes. Bake at 350 degrees for 10-12 minutes or until lightly browned. Remove, set on a wire rack, and let cool completely.
For the Filling: Put the 6 tbsp of butter, light brown sugar, and 1/2 tsp of kosher salt into a saucepan and cook over medium-low heat until melted and fully combined. Whisking, add in the Karo syrup, molasses, and bourbon. Beat eggs in a small bowl. Off heat, add 1/8 of a cup of the bourbon-sugar mixture to the eggs, whisking constantly to temper them so they do not scramble. Add a small amount of the bourbon mixture three to four more times to the eggs. Then pour the tempered egg mixture back into the saucepan and cook until glossy- about 2-3 more minutes. Off heat, pour in the vanilla. Fold in the toasted pecans.
Pour the filling into the cooled pie crust and place on a rimmed baking sheet. Bake for 40-45 minutes at 350 degrees until the pie is set.
Let the pie cool on a wire rack.
Serve with unsweetened freshly whipped heavy cream. The pie will keep up to two days in the fridge if well-wrapped with plastic.