Make the shortbread dough. Cream the butter and sugar together using a stand mixer or hand mixer on medium speed until light and fluffy, about 2 minutes. Add vanilla and beat on medium until incorporated. Gradually add the flour and beat on low speed until combined. Turn the mixer to high speed and beat for 1-2 minutes until dough becomes more breadcrumb like and less dry.
Bake the crust. Grease a 9-inch square pan with cooking oil spray and line with parchment paper, leaving an overhang on the sides to easily lift out the finished bars. Press the crumb mixture into the bottom of the lined pan and pack it in to form a single thin layer. Bake in a 350F preheated oven for 18-20 minutes until the edges are just starting to lightly brown. Remove the pan from the oven and add the pecan topping while the crust is still hot.

Make the pecan pie filling. While the crust is baking, prepare the pecan pie topping. In a large mixing bowl, whisk together brown sugar, flour, and salt. Then add maple syrup, eggs, and vanilla and whisk until smooth and combined. Stir in the pecans.
Bake. Pour the topping over the shortbread crust immediately once the crust is removed from the oven and is still hot. Return the baking pan back into the oven and bake for 40-50 minutes until the filling has set. You will know when it's set if the edges are set and the centre is slightly jiggly but not watery. The centre might also peak out but it will settle as it cools down.
Cool and serve. Allow the pecan pie bars to cool to room temperature, then cover and chill in the refrigerator for at least 1 hour (or overnight) before slicing. Once cooled, easily lift it out of the pan using the parchment paper overhang. Then, slice and serve.