Preheat your oven to 350°F (175°C). Grease a 9x9 inch baking pan with butter or line it with parchment paper.

In a medium bowl, whisk together the all-purpose flour, baking powder, ground cinnamon, and ground nutmeg until evenly combined.

In a large mixing bowl, combine the melted butter and brown sugar until smooth. Then, add the pumpkin puree, eggs, and vanilla extract, stirring until velvety.

Gradually fold the dry ingredients into the wet mixture, mixing until just combined.

Reserve a small portion of your batter, mix in more cinnamon and nutmeg, and swirl it into the main batter for added flavor.

Pour the batter into the baking pan and smooth the top. Sprinkle a mixture of granulated sugar and cinnamon over it.

Bake for 25–30 minutes, checking doneness with a toothpick.

Remove from oven and allow to cool in the pan for 10-15 minutes before transferring to a wire rack to cool completely.