Preheat your oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan, or line it with parchment paper.
In a large bowl, whisk together the melted butter and granulated sugar until well combined.
Beat in the eggs one at a time, then stir in the vanilla extract.
In a separate bowl, whisk together the cocoa powder, flour, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.
Pour the brownie batter into the prepared baking pan and spread it evenly.
In a small bowl, combine the brown sugar, melted butter, corn syrup, and vanilla extract for the topping. Stir until smooth.
Sprinkle the chopped pecans evenly over the brownie batter.
Drizzle the pecan pie topping mixture over the pecans and brownie batter. You can gently swirl it in with a toothpick if desired.
Bake for 25-30 minutes, or until a toothpick inserted into the center comes out with moist crumbs attached (not wet batter). Be careful not to overbake.
Let the brownies cool completely in the pan on a wire rack before cutting into squares.
Notes
For an extra rich flavor, you can add a handful of chocolate chips to the brownie batter. Ensure the brownies are fully cooled before cutting for cleaner slices.