Preheat your oven to 350 degrees F (175 degrees C) and line a 9x9-inch baking dish with parchment paper for easy removal and cleanup. Set aside.

In a large bowl, whisk together the melted butter and brown sugar until fully incorporated. This should take about 30 seconds of vigorous whisking.

Add in your pumpkin purée and vanilla extract. Whisk until the mixture is smooth and velvety, making sure no lumps remain.

In a separate bowl, combine your flour, cornstarch, pumpkin pie spice, baking powder, salt, and nutmeg. Whisk together until evenly distributed.

Gradually add the flour mixture to the wet mixture, stirring gently until fully combined. Avoid overmixing—the batter should be thick and smooth.

Pour the batter into the prepared baking dish, smoothing the top with a spatula.

In a small bowl, combine the granulated sugar and cinnamon. Sprinkle this mixture evenly over the top of the batter.

Place the dish in the oven and bake for 35-38 minutes. You’ll know they’re done when the edges turn golden brown and a toothpick inserted into the center comes out clean or with a few moist crumbs.

Allow the brownies to cool for about 10 minutes in the pan before transferring them to a wire rack to cool fully. Once cool, cut into squares and serve.