Step 1: Preheat your oven to 350°F (175°C) and grease an 8x8 inch baking pan or line it with parchment paper for easy removal.
Step 2: In a large bowl, whisk together the melted butter, granulated sugar, and brown sugar until well combined.
Step 3: Add the eggs one at a time, whisking well after each addition, then stir in the vanilla extract.
Step 4: Sift in the flour, cocoa powder, and salt. Gently fold the dry ingredients into the wet ingredients until just combined.
Step 5: Reserve about 1/2 cup of the brownie batter and spread the remaining batter into the prepared pan.
Step 6: In a small bowl, mix the pumpkin puree with the pumpkin pie spice and the reserved 1/2 cup of brownie batter.
Step 7: Dollop the pumpkin mixture over the chocolate batter in the pan. Use a knife to gently swirl the two mixtures together.
Step 8: Sprinkle the toasted chopped pecans evenly over the top of the batter.
Step 9: Bake for 30-35 minutes, or until a toothpick inserted into the center comes out with just a few moist crumbs.
Step 10: Allow the pumpkin pecan brownies to cool completely in the pan before slicing into squares.