Heat your oven to 350°F and line a rimmed baking sheet with foil (for spill overs).
Melt the chocolate and butter either in a double boiler or in 30-second increments in your microwave, then stir in the sugar, vanilla, eggs, flour, cocoa powder, and salt.
Grease a 9-inch deep dish pie pan or two standard size pie pans and pour 3/4 of the brownie in the pie pan (if using two, divide accordingly). Bake the brownie for 20 minutes in the pre-heated oven placed on top of the baking sheet.
While the brownie is baking prepare the pumpkin pie filling. In a medium bowl whisk together the pumpkin, heavy cream, egg, brown sugar, pumpkin spice and salt. Remove the brownie from the oven and carefully pour in the filling making sure not to overfill the pie. Take the remaining brownie and drop spoonfulls on the top of the pie, then swirl with a butter knife. Place the pie on the baking sheet back in the oven to bake for 35-40 minutes or until completely set in the center.
Let the pie cool completely before preparing the topping. At this point the pie can be made ahead of time and kept at room temperature for 1 day or in the refrigerator for a longer duration.
When ready to serve make the pecan topping by adding the brown sugar, maple syrup, butter, and pecans to a sauté pan over medium heat. Stir until the sugar has dissolved completely and the mixture has come to a boil. Stir in the heavy cream, bourbon, vanilla extract, and salt and bring back up to a boil. Cook for about 2-3 minutes until the sauce is nice and thick. Turn off the heat and let cool for about 10 minutes before spooning on top of the pie or serving on the side.