Step 1

Preheat the oven to 350 degrees Fahrenheit. Grease a 10 x 15-inch jelly roll pan.

Step 2

In a large bowl, stir together the flour, cinnamon, pumpkin pie spice, baking soda, baking powder and kosher salt. In a separate bowl, whisk together the eggs, then whisk in the brown sugar, granulated sugar, pumpkin puree, and oil. Pour the dry ingredients into the wet mixture and stir with a spatula until just combined. Pour the batter into the prepared pan and use a spatula to smooth it into an even layer.

Step 3

Bake for 25 to 30 minutes, until a toothpick inserted in the center comes out clean. Allow to cool for 30 minutes, then refrigerate about 15 minutes until it comes to room temperature. (Or allow to cool and refrigerate it, then frost before serving.)

Step 4

Meanwhile, make the cream cheese frosting: Let the butter and cream cheese sit on the counter for 1 hour to come to room temperature. Use a fine mesh sieve to sift the powdered sugar into a bowl. Beat the butter and cream cheese with a stand mixer or hand mixer on medium speed for 2 to 3 minutes until completely smooth, scraping once. Reduce the speed to low, then add the vanilla. Slowly add the powdered sugar until it comes together into a thick icing. Use immediately or refrigerate until using (stores refrigerated for up to 1 week; allow to stand at room temperature for 30 minutes and stir before using).

Step 5

Spread the frosting on top of the bars. If desired, dust with cinnamon. Serve immediately or store refrigerated. Stores refrigerated for up to 5 days. Freeze the completely cooled unfrosted bars tightly wrapped for up to 3 months.