Preheat oven to 350° F. Line an 8x8 pan with parchment paper and set aside.
In a medium bowl, whisk together the dry ingredients–flour, baking soda, salt and pumpkin pie spice. Set aside.
In the bowl of a stand mixer (or using a hand mixer), beat melted butter, brown sugar and sugar on medium-high speed until well combined and sugar is absorbed, about 2 minutes. Add egg, pumpkin puree and vanilla. Mix until incorporated. Scrape down the bottom and sides of the bowl as necessary.
Add dry ingredients to wet ingredients and mix just until combined (avoid over-mixing).
Transfer batter to prepared pan and spread evenly. Bake at 350° F for 20 to 25 minutes or until a toothpick inserted in the center comes out with little to no crumbs. Cool completely.
For the frosting, beat cream cheese and butter on medium-high speed until creamy and smooth, about 1 minute. Add confectioners’ sugar and vanilla, then mix until combined.
Frost cooled bars and garnish with a sprinkle of cinnamon. Slice and serve.
Notes
Pumpkin pie spice: Make your own by using 1 1/2 teaspoons ground cinnamon + 1/2 teaspoon ground ginger + 1/4 teaspoon ground nutmeg + 1/4 teaspoon ground cloves or all spice.Store frosted bars in an airtight container in the refrigerator for up to 5 days.Freeze bars individually wrapped in plastic wrap in an airtight container or freezer bag for up to 1 month.