Preheat the oven to 350°F (175°C) and grease a 9x9-inch baking pan.

In a large mixing bowl, whisk together the melted butter and brown sugar until well combined.

Add the pumpkin puree, egg, maple syrup, and vanilla extract to the bowl and mix until smooth.

In a separate bowl, combine the flour, baking powder, cinnamon, nutmeg, and salt.

Gradually add the dry mixture to the wet ingredients, stirring until just combined. Fold in white chocolate chips if using.

Pour the batter into the prepared baking pan, spreading it evenly.

Bake in the preheated oven for 25-30 minutes, or until a toothpick comes out clean.

Allow the blondies to cool in the pan for about 10 minutes before transferring to a wire rack.

Once cooled, cut into squares and serve.