Gather the ingredients.
Preheat the oven to 350°F and line your baking sheets with parchment paper.
Whisk the dry ingredients together until combined.
In another bowl, mix the brown sugar and oil. Whisk in the pumpkin puree.
Add the eggs and vanilla extract to the pumpkin mixture and mix until incorporated.
Add the flour mixture to the wet ingredients, half a cup at a time, until a dough forms.
Portion the dough with a tablespoon and drop it onto the prepared baking sheets, about an inch apart.
Bake the cookies for 15 minutes.
Let the cookies cool on the baking sheet for 10 minutes, then transfer them to a wire rack to cool completely.
Beat the marshmallow filling ingredients together on medium speed for 3 minutes or until smooth.
Spread a tablespoon of marshmallow fluff filling on the flat side of one cookie, then top with another cookie.
Repeat with the remaining cookies and filling.