Preheat the oven according to the brownie mix package directions. Lightly grease a 9x9-inch baking pan or line it with parchment paper.
Prepare the brownie mix according to the package directions. Spread the batter evenly into the prepared pan.
Bake for about 20–25 minutes, or until the brownie layer has started to set around the edges and has developed a thin crust on top. The center should still be underbaked.
While the brownies bake, whisk together the corn syrup, granulated sugar, melted butter, eggs, vanilla and salt until smooth.
Stir in the chopped pecans until evenly coated in the filling.
Remove the partially baked brownies from the oven. Carefully spoon the pecan mixture evenly over the top, spreading the pecans all the way to the edges.
Return the brownies to the oven and bake for another 25–30 minutes, or until the pecan topping is set around the edges. The very center can still have a slight jiggle.
Allow the brownies to cool in the pan for at least 2 hours before slicing. The pecan pie topping will continue to set as it cools.
Cut into 12 large or 16 smaller squares and serve.