To make the pumpkin bars: Preheat the oven to 350°F (180°C). Spray a 10x15-inch jelly roll pan with nonstick cooking spray, line with parchment paper (this is optional, but makes it easier to remove the bars from the pan), and set aside.
In a large mixing bowl, whisk together the flour, baking powder, baking soda, pumpkin pie spice, ground cinnamon, and salt until well combined. Set aside.
In a separate mixing bowl, whisk together the melted butter, pumpkin puree, brown sugar, granulated sugar, eggs, and vanilla extract until fully combined.
Add the dry ingredients to the wet ingredients and mix until just combined, making sure not to over mix the batter.
Pour the batter into the prepared baking pan and spread it around into one even layer. I like to use an offset spatula for this step.
Bake for 17 to 23 minutes or until a toothpick inserted into the center comes out clean.
Remove from the oven and set aside to cool completely.
To make the cream cheese frosting: In the bowl of a stand mixer fitted with the paddle attachment or in a large mixing bowl using a handheld mixer, beat the cream cheese and butter until smooth.
Add the powdered sugar and vanilla extract and mix on medium speed until fully combined and smooth, stopping to scrape down the sides of the bowl as needed.
To assemble the bars: Scoop the cream cheese frosting onto the cooled pumpkin bars and use an offset spatula (or the back of a spoon) to smooth it out into one even layer.
Slice into bars and serve or refrigerate until ready to serve.
Video
Notes
Storage Instructions: Bars may be stored in an airtight container in the fridge for up to 5 days.Freezing Instructions: Bars may be frozen for up to three months, with or without the frosting. If freezing the bars after they've been frosted, I recommend freezing them first on a parchment paper-lined baking sheet. Once the bars have hardened (after one to two hours), transfer them to a freezer bag. Thaw overnight in the refrigerator.