Preheat oven to 350°F (175°C). Line a 9"x13" (23x33cm) baking pan with parchment paper with an overhang on all sides. Set aside.
Make the shortbread crust in a food processor: Place flour, sugar, salt, and butter in a food processor and pulse until it starts to clump. Transfer to the prepared baking pan and press with your fingers evenly into the bottom of the pan. Bake for 20 minutes until crust is lightly browned.
If you don't have a food processor, then make the shortbread crust with a pastry cutter or two forks instead: In this case mix together flour, salt, and sugar in a large mixing bowl. Then add butter and cut it into the mixture until it starts to clump.
While the crust is baking, prepare the pecan filling: Over medium-high heat, in a medium-sized sauce-pan, combine brown sugar, maple syrup, heavy cream, salt, vanilla*, and butter and bring to a simmer. Cook for 1 minute and stir constantly. Remove from heat and stir in the chopped pecans.
Remove crust from the oven and pour pecan mixture over the crust evenly. Then return to the oven and bake an additional 20-25 minutes. The longer you bake them the harder and dryer the filling will be. I baked the filling for exactly 20 minutes.
Remove pecan pie shortbread bars from the oven and let cool completely. Then lift them out of the pan with the paper and cut into 20 bars. Store in an airtight container at room temperature for up to 3 days.