Preheat your oven to 350°F (175°C) and grease an 8×8-inch baking pan or line it with parchment paper.
In a large bowl, combine the pumpkin puree, sugar, and eggs. Mix well until the ingredients are incorporated.
In another bowl, whisk together the flour, cocoa powder, baking powder, and salt. Gradually add the dry mixture to the wet mixture, stirring just until combined.
Stir in the vanilla extract and any optional add-ins like chocolate chips or nuts.
Pour the brownie batter into the prepared baking pan, smoothing the top evenly.
Bake in the preheated oven for about 25-30 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
Let the brownies cool in the pan for about 15 minutes, then transfer them to a wire rack to cool completely before cutting into squares.