In a large heat-proof bowl, combine the butter, sugar, cocoa powder and salt, and melt in the microwave in 30 second-intervals, stirring in between each interval, until the butter is melted (or melt in a small saucepan over medium-low heat). If the mixture appears gritty, that’s ok. If the mixture is hot, set aside for a few minutes until it’s warm.
While brownies are baking, make the pecan layer: Heat butter, sugar, and corn syrup/maple syrup together in a saucepan, stirring constantly, until sugar dissolves. Let mixture cool slightly, then whisk in the rest of the ingredients, adding the chopped pecans last. Mix until combined. Gently pour the pecan mixture over the baked brownie, using a spoon or small offset spatula to carefully spread all the way to the edges. Bake until the pecan pie layer is golden and appear set, 20 to 25 minutes. Allow to cool completely on a wire rack. I recommend letting it set in the fridge for a few hours before slicing into squares.