Preheat your oven to °350F. Line an 8x8-inch baking pan with non-stick foil or parchment paper. (Or you can coat it with Wilton Cake Release or non-stick spray)
In a large mixing bowl, stir together the brownie mix and the pumpkin puree. (The mixture will be thick.)
Pour the mixture into your prepared pan and level the top. (I found an offset spatula like you use to frost a cake with was the easiest way to spread it evenly.)
Bake at 350°F for 15 to 18 minutes. Test for doneness, they're thick and fudgy so some crumbs will remain on the wooden pick even when done.
Store in an airtight container in the fridge for 5 to 6 days. Because these brownies are so moist, I recommend refrigerating them.