In a large mixing bowl, or bowl of a stand mixer, combine the gluten-free flour, coconut sugar, and pumpkin pie spice. Stir to blend.
In a separate medium bowl, whisk together the melted coconut oil, pumpkin puree, maple syrup (or egg yolk), and vanilla extract until creamy.
Pour the wet ingredients into the bowl with the flour mixture and beat until a dough is formed. The dough will be crumbly, but should hold together when you squeeze it.
Using your hands, gather the dough into a ball and wrap in plastic wrap. Refrigerate for 10 to 15 minutes.
Meanwhile, preheat the oven to 350 degrees F. Line baking sheets with parchment paper.
Once chilled, place the ball of dough between two sheets of parchment paper. Use a rolling pin to roll out the dough until about 1/3- to 1/2-inch thick. If you don't have a rolling pin, you can use a wine bottle. Remove the top sheet of parchment paper.
Using a pre-greased 2-inch circle cookie cutter (or cookie cutter of desired shape and size) cut out cookies, and use a pre-greased spatula to place them gently on the baking sheets. Do this until all of the dough is used up. You should have at least 20 to 22 cookies which will make 10 to 11 sandwich cookies
Bake the cookies for 8 to 10 minutes until they have started to firm (they might still be soft to the touch, but they will continue to firm as they cool). Allow the cookies to completely cool before filling (1-2 hours).
Make the frosting. In a large bowl, combine the butter and cream cheese. Using a whisk or a hand-beater (or hand-blender with the whisk attachment), cream together the butter and cream cheese until blended and fluffy, about 30 seconds. Add the powdered monk fruit and vanilla extract and blend again. Use your spatula to give the filling mixture a stir.
Place 1-2 tablespoons of filling between two cookies and press them together until the filling reaches the edges of the cookies. Continue to do this until all of the cookies have been filled. Keep the cookies in the refrigerator.