Preheat the oven to 350 degrees Fahrenheit (180 degrees Celsius) and grease or line a square baking pan with parchment paper. Leave about 2 inches of paper hanging over the sides and set aside.
Melt the bittersweet chocolate and unsalted butter in the microwave in a heatproof bowl, stirring every 30 seconds until completely melted.
Beat the granulated sugar, brown sugar, eggs, and vanilla extract together in a large bowl with a hand mixer on medium high speed until frothy and pale yellow. Then mix in the pumpkin puree.
200 grams granulated sugar, 55 grams brown sugar, 3 large eggs, 2 teaspoons vanilla extract, 120 grams pumpkin puree
While mixing on medium speed, stream in the melted chocolate mixture. Continue mixing until well combined.
Gradually add the flour, cocoa powder, pumpkin pie spice, and salt to the wet ingredients. Mix on low speed until there are no dry patches, then mix in the chocolate chips.
94 grams all purpose flour, 43 grams cocoa powder, 1 tablespoon pumpkin pie spice, ½ teaspoon salt, 100 grams semi-sweet chocolate chips
Pour the brownie batter into the prepared pan and spread it into an even layer. Bake for 30-40 minutes or until a toothpick inserted in the center comes out with a sticky layer of chocolate crumbs, but no wet batter.
Remove the pan the oven and let cool for 5-10 minutes before transferring to a wire rack to cool completely.
Once the brownies are completely cool, slice and enjoy!
Notes
Measure the flour and cocoa powder in a grams with a digital kitchen scale for the best results. If you don't have a scale, fluff up the flour in the bag and gently spoon it into a measuring cup. Once overflowing, swipe off the excess.Use room temperature eggs so they mix in easily with the other ingredients.Storage: Place the brownies in an airtight container and store at room temperature for up to 5 days.Freezing: Transfer brownies to a freezer-safe sealed container or bag. Freeze for up to 3 months. Thaw overnight in the refrigerator before enjoying.