Preheat your oven to 350 degrees Fahrenheit. Grease a 9×9 inch baking pan with non-stick spray and line it with parchment paper. Set aside
Prepare the boxed brownie mix according to the package instructions. This usually involves combining the mix with eggs, oil, and water. Mix until well combined and set aside.
Begin by removing excess moisture from the pumpkin puree. Place the pumpkin puree in a cheesecloth and squeeze out the liquid into a small bowl. Repeat this process a couple of times to achieve a thicker, more cohesive texture, resembling play dough. Discard the pumpkin water. You will end up with ¼ cup of pumpkin after the moisture is removed.
In a medium bowl, whisk together the all-purpose flour, pumpkin pie spice, ground cinnamon, baking soda, baking powder, and salt. Set aside this dry mixture.
In another medium-sized bowl, using an electric hand mixer, beat the melted butter, brown sugar, and granulated sugar together until the mixture becomes light and fluffy. This should take about 3 minutes.
Whisk in the large egg and egg yolk one at a time, mixing each for about 30 seconds. After incorporating the eggs, add the vanilla extract and the prepared, well-drained pumpkin puree. Mix on low just until the ingredients are combined.
Switch to a rubber spatula and gently fold the dry flour mixture and chocolate chips into the wet batter. Mix until there are no longer any visible signs of flour, being careful not to overmix. If all the moisture has been removed from the pumpkin, the dough will have a somewhat thick consistency.
Using two spoons, alternate between the brownie batter and cookie dough by dropping small balls or dollops (the smaller the better this helps create that beautiful brookie look) into the prepped pan until you used both the cookie dough and the brownie batter. Try to evenly distribute the two throughout.
Bake in the for 30-35 minutes depending on your oven, or until a toothpick inserted into the center comes out with moist crumbs.
Remove from the oven and let the brookies cool in the pan until you are ready to serve.
Serve and enjoy the deliciousness of your homemade brookies!
Notes
It is really important to do this step. If you don't do it, your brookie will have more of a cake texture and not a chewy cookie like. You can also use paper towels to remove moisture!