In a medium bowl add the flour, baking soda, rolled oats, salt, cinnamon, and nutmeg. Whisk and set aside.
Using a hand mixer combine the softened butter, brown sugar, and granulated sugar until combined. Slowly add the eggs one at a time. Follow this up with the vanilla extract, molasses (or dark corn syrup) and pumpkin puree. Once everything is mixed slowly add the flour mixture.
Chill dough for 10-15 minutes and preheat your oven to 350. Bake the cookies for 10-12 minutes and let the cookies cool for a few minutes before transferring to a cooling rack. Use a toothpicks to poke the cookies and see if they're fully cooked. If not, pop them in for another 2-3 minutes.
As the cookies are cooling begin making your Marshmallow fluff frosting. You will use a piping bag to add the frosting to each cookie. Pipe the frosting on one cookie and place another on top to make the oatmeal cream pie. Chill the oatmeal cream pies in your refrigerator for 10 minutes before serving.