Preheat your oven to 350°F and thoroughly grease a 9×13-inch metal baking pan, or line it with a sheet of parchment paper leaving a 1-inch overhang on the long sides to act as a sling for easy removal.

In a medium mixing bowl, combine the all-purpose flour, powdered sugar, and a pinch of salt, whisking to distribute the dry elements evenly.

Drop the 1 cup of cold, cubed butter into the flour bowl. Use a pastry cutter, two knives, or your fingertips to aggressively cut the fat into the flour until the mixture breaks down into uniform, pea-sized crumbs that resemble coarse sand.

Dump the shaggy dough crumbs directly into your lined 9×13-inch pan. Use the flat bottom of a measuring cup or your clean hands to firmly compress the mixture into a flat, tightly packed, and even layer across the entire bottom of the dish.

Bake the crust baseline uncovered at 350°F for 15 minutes just until the surface tension sets and the edges turn a very pale, light golden color, then remove the pan from the oven.

While the crust pre-bakes, prepare the pecan custard layer. In a large mixing bowl, beat the 3 large eggs, packed brown sugar, corn syrup (or alternative syrup), 2 tablespoons of melted butter, and vanilla extract together with a whisk or electric hand mixer for 1 full minute until smooth, completely unified, and slightly frothy.

Stir the 1 ½ cups of coarsely chopped pecans directly into the liquid egg and sugar slurry, tossing until every nut piece is fully coated.

Pour the sticky pecan mixture uniformly over the hot, par-baked shortbread crust, using a silicone spatula to spread the nuts into a single, level layer across the pan.

Return the pan to the middle rack of the oven and bake uncovered at 350°F for 25 to 30 minutes. Watch the center closely; the bars are finished the exact moment the outer edges are set and bubbling, and the center gives a very slight, firm jiggle without looking fluid or liquid.

Remove from the oven and set the pan on a wire rack to cool completely at room temperature for at least 1 hour, then transfer to the refrigerator for 1 additional hour. This chilling window is essential to let the hot sugar lipids and egg proteins fully stabilize and tighten. Lift the bars out using the parchment paper handles and slice cleanly into sharp squares with a hot knife.