• Preheat your oven to 350℉. Spray a 9x13-inch baking pan with cooking spray then line it with parchment paper, but with the parchment paper hanging off the sides to make it easy to lift out bars.

Crust

• Add all the crust ingredients to a large bowl and using a pastry cutter or two forks, blend everything together until it resembles a dry coarse meal. Alternatively, you could use a food processor.
  
• Transfer the crumb mixture to the prepared baking dish and press it down evenly into the bottom. Place the pan into the oven and bake it for about 20 minutes, until the curst is set and dry on top, but it hasn't yet browned. Let the crust cool completely before adding the filling.
  

Filling

• In a large bowl add the flour, brown sugar, salt and whisk everything together. This will ensure there will be no lumps. Add the lemon zest and whisk. Add the corn syrup, eggs, vanilla, and whisk everything together until well combined. 
  
• Fold in the chopped pecans. Let the mixture rest while the crust bakes and cools. During this time the pecan mixture will slightly thicken.
  
• Pour the pecan filling over the prepared crust and use a spatula to spread the pecans evenly, if needed. Place the pan in the oven and bake for 40 to 50 minutes or until the filling is set. To check if the filling is set, shake the pan and if the center is not wobbly then it's done.
  
• Cool completely at room temperature, then place the pan in the fridge for several hours or overnight before cutting them.
• The next day, use the parchment paper to gently lift the bars from the pan, then cut into squares using a sharp serrated knife. I cut it into 24 pieces, but you can cut it into 12 if you wish for larger squares.