Preheat oven to 350ºF. Line a 9-inch square baking pan with parchment paper, overlapping the sides an inch or two. Spray parchment paper with nonstick cooking spray.
In a large bowl, stir together melted butter, granulated sugar and brown sugar until well combined.
Mix in eggs and vanilla, one at a time, until well combined.
Mix in cocoa powder, baking soda and salt until well combined.
Stir in flour just until combined.
Spread batter into prepared baking pan. Bake just until top is set, about 25 minutes.
Meanwhile, prepare pecan topping.
When brownie top is set, remove from oven. Gently pour pecan topping around the outer perimeter of brownies, to avoid making brownies sink in the middle. Evenly distribute the pecan topping over the top gently with a spoon.
Return the brownies to the oven and continue baking until the topping is set, about 20-25 minutes. Brownies will stop jiggling and topping will look deep golden brown. Toothpick inserted inside will have a few moist crumbs on it. (If your topping starts to brown too much on the edges before the inside is done, apply aluminum foil around the edges as you would with a pie.)
Remove from oven and cool completely before cutting, about 2- 2 1/2 hours.
Cut into squares, wiping knife between cuts.
Pecan Topping
In a medium bowl, stir together maple syrup, butter, brown sugar, egg, maple extract and salt until well combined.
Stir in pecans until well coated with maple syrup mixture.