Preheat the oven to 350°F. Line a 9 x 13 inch baking pan with parchment paper. Allow the parchment to extend 2 inches over the sides of the pan for easy removal of the bars once baked. Set aside.

Spread the pumpkin puree on a large plate and lay a paper towel over the top of it to remove the moisture. Use a second paper towel to blot the pumpkin once more if needed. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment (or using a handheld mixer), cream together the butter and sugars on medium-high speed for 2 to 3 minutes until light and fluffy. Scraped down the sides of the bowl. 

Add the egg yolk, pumpkin and vanilla. Mix to combine well.

In a medium bowl, whisk together the flour, baking soda, baking powder, salt, cinnamon, ginger, cloves, allspice and nutmeg. 

Add the dry ingredients to the pumpkin and butter mixture, mixing on low speed just until combined. Do not overmix.

Remove the bowl from the stand mixer and use a large spatula or wooden spoon to stir in 1 1/2 cups of the chocolate chips, again being careful not to overmix.

Transfer the dough to the prepared pan and use an offset spatula to press the dough evenly across the pan, leveling the top. Sprinkle the remaining 1/4 cup of chocolate chips across the top. Add more if desired. 

Bake for 25 to 30 minutes or until the edges are set, the top is golden brown and a toothpick inserted in the center of the pan comes out mostly clean or with a few moist crumbs remaining.

Remove the pan from the oven and cool the bars on a wire rack before cutting into squares.