Preheat oven to 350°F. Line cookie sheets with parchment paper.
In a medium sized bowl, whisk together flour, baking soda, baking powder, pumpkin pie spice and salt.
Using a stand mixer beat sugar, brown sugar and butter together. Scrape down the sides as needed. Add in pumpkin, egg and vanilla extract and beat again. Scrape down the bowl to incorporate everything evenly.
Slowly add in dry ingredients and chocolate chips. Stir just until combined. Do not over mix.
Scoop out dough balls roughly the size of a heaping tablespoon, place them on cookie sheets and bake for 15 minutes. Let cool.
Prepare the filling by combining the marshmallow fluff, confectioners’ sugar, shortening and vanilla extract in the bowl of a stand mixer and mix until completely combined. Add milk as necessary to get to a soft (but not too soft consistency.)
Frost the bottoms of half of your cookies to make your cookie sandwiches. Top with a “blank” cookie and serve.