Preheat your oven to 350°F (175°C). Grease and line the 9x13 inch baking pan with parchment paper for easy removal.

In a medium mixing bowl, whisk together the flour, cocoa powder, baking powder, and salt. Set aside.

In a large mixing bowl, cream the softened butter, brown sugar, and granulated sugar together until light and fluffy. This should take about 3-5 minutes with an electric mixer.

Add the eggs one at a time to the butter mixture, mixing well after each addition. Then, mix in the pumpkin puree and vanilla extract until well combined.

Gradually add the dry ingredients to the wet mixture, stirring until just combined. Do not overmix.

Fold in the cinnamon, nutmeg, ginger, chocolate chips, and nuts if using.

Pour the batter into the prepared pan, spreading it evenly. Bake in the preheated oven for about 30-35 minutes, or until a toothpick inserted in the center comes out clean.

Remove the pan from the oven and allow the bars to cool in the pan for about 15 minutes. Then, transfer to a cooling rack to cool completely before cutting into bars.

For added flavor, you can sprinkle some additional chocolate chips or nuts on top before baking.

These bars can be stored in an airtight container for up to one week.

Serve with a dollop of whipped cream or a scoop of vanilla ice cream for an extra special treat.