To prepare the cookies:

1. Preheat the oven to 350 degrees Fahrenheit and line 2 sheet pans with parchment paper.
2. In a large bowl or the bowl of a stand mixer, cream the butter and brown sugar until smooth and combined, about 1-2 minutes. Add the egg, molasses, and vanilla and stir to combined. Scrape the sides of the bowl and add the remaining ingredients. Stir on low just until well-combined.
3. Use a small cookie scoop to spoon 2 teaspoon sized rounds of dough 2” apart on the prepared cookie sheets. Bake one at a time in the preheated for about 9 minutes or until the edges are set and turning golden. The center of the cookie may still look wet. Remove from oven and allow to cool completely. If you notice your cookies look wonky upon removal from the oven, use the rim of a large glass or jar to nudge them into a rounder, perfected shape. Be sure to do this carefully while they are still fresh from the oven. Continue baking the remaining cookies and allow to cool completely.

To prepare the filling:

1. Cream the butter and powdered sugar together on medium speed in a large bowl using a hand mixer. Add the marshmallow fluff and stir until well combined. If needed, you can thin the frosting out slightly with a teaspoon or two of water- be careful not to add to much though as this makes for a messy cookie. Spoon the filling into a piping bag fitted with a medium round tip and sandwich the cream in between two cookies of the same size. Alternatively, you can just spread large dollops on with a knife. Enjoy!