Preheat your oven to 350°F (175°C). Line a 9x13-inch baking pan with parchment paper, leaving an overhang on the two long sides to act as handles for easy removal later. Lightly grease the paper and any exposed sides of the pan.

In a large bowl, whisk together the all-purpose flour and powdered sugar.

Add the cold, cubed butter to the flour mixture. Using a pastry blender or your fingertips, cut the butter into the flour until the mixture resembles coarse, sandy crumbs.

Stir in the vanilla extract. The dough will be crumbly. Press the dough firmly and evenly into the bottom of the prepared pan.

Bake for 18-20 minutes, or until the edges are lightly golden brown. Remove from the oven and set aside while you prepare the filling. Keep the oven on.

In a medium saucepan over medium heat, combine the packed brown sugar, corn syrup, and melted butter. Bring the mixture to a gentle boil, stirring constantly. Once it boils, remove it from the heat and let it cool for about 5 minutes.

In a separate medium bowl, whisk together the lightly beaten eggs, vanilla extract, and salt.

Very slowly, pour the warm brown sugar mixture into the egg mixture while whisking constantly. This tempers the eggs and prevents them from scrambling. Continue whisking until the mixture is smooth and well combined.

Stir in the chopped pecans until they are evenly coated.

Pour the pecan filling evenly over the warm, par-baked shortbread crust. Use a spatula to spread it to the edges.

Return the pan to the 350°F (175°C) oven and bake for 25-30 minutes, or until the filling is set and the center only has a slight jiggle. The top will be a deep golden brown.

Remove the pan from the oven and place it on a wire rack to cool completely. This is a crucial step and will take at least 3 hours. Do not attempt to cut the bars while they are still warm.

Once completely cooled, use the parchment paper overhangs to lift the entire slab out of the pan. Place it on a cutting board and cut into 24 bars. Serve at room temperature.