For the Crust
Preheat your oven to 350 degrees. Line a 10.5 x 7-inch baking dish, with a foil sling allowing the foil to hang over each side. Spray generously with cooking spray. Set aside.
In a food processor, add in the flour, brown sugar, pecans, baking powder, and salt. Pulse 5-6 times until combined and pecans are finely chopped like sand.
Add in the butter and pulse another five seconds until the mixture is like cornmeal.
Press the mixture into the foil-lined baking dish using the back of a measuring cup to even out the mixture. Be sure to press the crust up the sides and evenly around the pan.
Bake at 350 degrees for 20 minutes.
For the Filling
While the crust is baking, in a medium bowl, combine the brown sugar, Karo syrup, maple syrup, rum, butter, salt, and vanilla with a whisk. Whisk in the egg until the mixture is smooth.
Pour the mixture into the warm crust.
Top the filling with the 2 cups of coarsely chopped pecans.
Bake at 350 for 15 minutes. Rotate the pan and bake for another 10 minutes.
Set the dish on a wire rack to cool for 30 minutes.
After 30 minutes, remove the bars using the foil slings and let cool for another 1 1/2 hours until the crust is completely cooled and the filling is set.
Peel the foil off of the bars and using a serrated knife, cut into 12 equal pieces. Cooled bars can be stored in an airtight container for five days... but they won't last that long.