Preheat oven to 350* F. In an 8x8 pan place a piece of parchment paper that covers the bottom and up the side of the pan. *This allows you to easily pull the pecan pie bars out of the pan once they are cooled and ready to slice*
In the bowl of a food processor, or a medium bowl using a handheld mixer, add the softened butter, flour, sugar, salt, and vanilla extract. Pulse together until the dough begins to come together. You should be able to squeeze the dough together and it will stay and not crumble.
Press the dough into an even layer in the bottom of your prepared 8x8 pan. Bake the crust for 10 minutes.
Make your filling by adding, to a small saucepan, the ¼ cup butter, granulated sugar, Karo syrup, and maple syrup. Cook on medium heat for 3-4 minutes or until the sugar is dissolved and it is a light golden color. Turn off the heat and whisk in the salt and flour until no lumps remain.
In a separate bowl, whisk the eggs and vanilla then, very slowly, pour the warm sugar mixture into the eggs while continuing to whisk constantly. *You want to really make sure you go slow with pouring in the warm sugar into the eggs so that the heat does not scramble your eggs.* Whisk until your filling is completely combined.
Add your chopped pecans to the filling mixture and stir. Gently pour the filling mixture onto the shortbread crust once it comes out of the oven.
Return the pan to the oven and continue to bake your pecan pie bars for an additional 30-35 minutes or until the top is golden and the center has set.
Cool your pecan pie bars on the counter until they are room temperature. If you try to cut your bars before they are completely cool then the filling may run and not be set up.