Preheat the oven to 400° Place parchment paper, cut to fit on your baking sheet.
Combine flour, oatmeal, baking powder, baking soda, cornstarch and all dry spices. Set aside.
In a separate large bowl, combine butter and brown sugar with an electric mixer on high speed until creamy. Add in eggs, one at a time, mixing after each addition. Mix in vanilla extract.
Add the dry ingredients and the pumpkin into the wet ingredients. Mix until thoroughly combined.
Place rounded tablespoonfuls of cookie batter, two inches apart on the baking sheet. Flatten the cookie slightly with a drinking glass or the bottom of your measuring cup.
Bake on center rack of oven for approx. 10-12 minutes. Remove cookies to a wire cooling rack. Cool completely.
Filling
Whip marshmallow creme and butter until fluffy.
Add vanilla and powdered sugar and whip until thoroughly combined.
Chill the filling until it sets up a bit. (about 1 hour)
Place approx. 1 tbsp. of filling on half of the pies and place the remaining ones on the top of each one.