Preheat your oven to 350°F (175°C).
Prepare a 9×9 inch baking pan by greasing it with butter or lining it with parchment paper.
In a separate bowl, whisk together the all-purpose flour, baking powder, ground cinnamon, and ground nutmeg.
In a large mixing bowl, combine the melted butter and brown sugar, then add the pumpkin puree, eggs, and vanilla extract, mixing until smooth.
Gradually add the dry mixture to the wet ingredients, stirring gently until just combined.
Create a pumpkin spice swirl by mixing a small amount of the batter with additional cinnamon and nutmeg, then swirl it into the main batter.
Pour the batter into the prepared baking pan and sprinkle the cinnamon sugar mixture on top.
Bake for 25-30 minutes, checking for doneness with a toothpick.
Let the blondies cool in the pan for 10-15 minutes before transferring to a wire rack to cool completely before cutting into squares.