Preheat your oven to 350°F (180°C), or 160°C for a fan oven. Line a 9×9 inch (23×23 cm) baking pan with parchment paper.
In a large bowl, whisk together the melted butter and granulated sugar until smooth. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Sift together the all-purpose flour and salt. Fold the dry mix into the wet ingredients until no dry streaks remain.
Divide the batter into two bowls. Stir pumpkin puree and pumpkin pie spice into one half, and mix cocoa powder into the other half.
Alternate scoops of the pumpkin and chocolate batters in the prepared pan. Use a knife to swirl gently.
Sprinkle semisweet chocolate chips on top. Bake for 25 to 30 minutes until a toothpick comes out clean.
Allow to cool completely in the pan before cutting into squares.
