Melt stick of butter in microwave-safe bowl. Once melted, mix in the sugars and set aside.
In a large bowl, combine flour, pumpkin spice, cinnamon, salt, and baking powder.
After letting melted butter-sugar mixture cool for a few minutes, add this into your dry mixture.
Mix an egg, the pumpkin puree, and vanilla into flour mixture.
Grease a 9x9 square pan with non-stick cooking spray (or line with criss-crossed parchment paper for easy removal.)
Spread mixture evenly in your pan and then bake for 20-22 minutes.
While bars are cooling, make your cream cheese frosting. In a stand mixer with the paddle attachment, beat butter and cream cheese on medium speed until softened, about 3 minutes.
Beat in the vanilla and gradually add in powdered sugar, one cup at a time, until fully combined and frosting has reached desired consistency.
Spread your cream cheese frosting on bars (once fully cooled) with an offset spatula.
Cut into 16 squares, serve, and enjoy!
Notes
This recipe was written for high altitude kitchens (5280 feet.) If at sea level, increase baking powder to 1 tsp and decrease pumpkin puree by 2 TBSP.