• Preheat the oven to 325°F. Grease a square 9x9-inch baking pan with nonstick cooking spray and line it with parchment paper, letting the paper overhang for easy removal.
  

Pre-Bake The Brownies:

• Prepare the brownie batter according to the package instructions and scrape the batter into the prepared pan.
  
• Bake for about 25 minutes, until the edges look set and the top is mostly matte but the center still looks slightly soft and shiny. If the surface is still glossy and jiggles like raw batter, bake for 3 to 5 minutes longer. The brownies should be just underbaked in the center, as they will finish baking when they go back in the oven with the pecan topping.

Prepare The Pecan Topping:

• In a medium saucepan over medium heat, melt the unsalted butter with the packed brown sugar, light corn syrup, heavy cream, vanilla extract, and salt.
• Cook, stirring constantly, until the sugar has dissolved and the mixture looks slightly thickened and glossy, 2 to 4 minutes. Do not let it boil vigorously.
• Stir in the chopped pecans and cook for 30 to 60 seconds, just until evenly coated.

Assemble And Finish Baking:

• Remove the brownies from the oven and set the pan on a heatproof surface. Increase the oven temperature to 350°F.
• Carefully spread the warm pecan mixture evenly over the brownie base, nudging it gently into the corners without tearing the top.
  
• Return the pan to the oven and bake until the pecan topping is bubbling across the surface, including the center, and the edges look deep golden-brown, 25 to 35 minutes. The topping should look set and no longer liquid when you gently tilt the pan.

Cool, Slice, And Serve The Dish:

• Transfer the pan to a wire rack and let cool completely, 1 to 2 hours, until the topping is set and no longer warm to the touch. This helps the layers firm up for cleaner slices.
• Use the parchment overhang to carefully lift the brownies from the pan and onto a cutting board. Use a sharp knife to cut into squares, wiping the blade clean between cuts for neat edges.