Preheat your oven to 350°F (175°C) and line a 9x9 inch baking pan with parchment paper.
In a large mixing bowl, combine the melted butter and brown sugar, whisking until smooth.
Add the pumpkin puree, maple syrup, eggs, and vanilla extract, mixing until well combined.
In a separate bowl, whisk together the flour, baking powder, salt, cinnamon, and nutmeg.
Gradually add the dry mixture to the wet mixture, stirring until just combined; be careful not to overmix.
Fold in the chopped nuts, if using, ensuring they are evenly distributed throughout the batter.
Pour the batter into the prepared pan, smoothing the top with a spatula.
Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
Remove from the oven and allow to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.
Once cooled, cut into squares and serve; enjoy your delightful Pumpkin Maple Blondies!