Preheat the oven to 350°F (180°C). Line a 9×9-inch baking pan with parchment paper, leaving an overhang on the sides for easy lifting.
In a medium bowl, mix flour, sugar, and salt. Cut in the cold butter with a pastry cutter or fork until the mixture resembles coarse crumbs. Press evenly into the prepared pan.
2 cups all-purpose flour, ½ cup sugar, ½ teaspoon salt, 1 cup cold butter
Bake for 20 minutes, or until lightly golden.
In a large bowl, whisk the eggs. Add corn syrup, brown sugar, melted butter, and vanilla. Whisk until smooth, then stir in the pecans.
4 large eggs, 1 ½ cups light corn syrup, 1 ½ cups packed brown sugar, 3 tablespoons butter, 2 teaspoons vanilla extract, 2 ½ cups chopped pecans
Pour the filling over the hot crust. Return to the oven and bake for 25–30 minutes, or until the center is just set (it should jiggle slightly).
Let cool completely in the pan for at least 2 hours before cutting into bars. The filling will firm up as it cools.