Cream the butter and sugars by combining unsalted butter, brown sugar, and granulated sugar in a stand mixer. Beat until light and fluffy.

Add the egg, molasses, and vanilla extract to the creamed mixture. Mix until just combined.

Whisk together flour, baking soda, cinnamon, and salt in a separate bowl. Gradually add to wet mix.

Fold in quick oats gently with a spatula.

Preheat oven to 375°F (190°C). Scoop dough onto a baking sheet lined with parchment paper.

Bake for 12-14 minutes until slightly underbaked. Allow to cool on the baking sheet for 5 minutes, then transfer to a wire rack.

Prepare the cream filling by mixing together butter, powdered sugar, marshmallow crème, salt, and vanilla. Adjust with heavy cream.

Once cookies are cool, pipe filling onto one cookie and top with another, pressing gently.

Store in an airtight container at room temperature or refrigerate.