Preheat the oven according to the directions on the brownie mix box. Prepare the brownie batter using the ingredients listed on the package, then spread it evenly into the recommended baking pan.
Bake the brownies according to the package directions. While they are baking, start making the pecan pie topping.
Add the butter, brown sugar, and corn syrup to a medium saucepan over medium heat. Cook, stirring often, until the butter has melted and the brown sugar has dissolved.
Stir in the cornstarch until everything is well combined. Let the mixture gently come to a boil, then remove the pan from the heat.
Stir in the salt, cinnamon, and pecans until the pecans are completely coated in the brown sugar mixture.
When the brownies are done with their first bake, remove them from the oven. Reduce the oven temperature to 325°F.
Spoon the pecan topping evenly over the brownies, spreading it all the way to the edges.
Return the brownies to the oven and bake for another 15 minutes, or until the pecan topping is bubbling and starting to set.
Let the brownies cool completely before slicing. This gives the pecan layer time to firm up and makes the brownies much easier to cut.
Cut into 9 large brownies or smaller squares and serve.