Preheat your oven to 325°F (162°C) and line two baking sheets with parchment paper.

In a stand mixer, cream together unsalted butter, light brown sugar, and molasses until creamy and smooth.

Add the egg and vanilla extract, mixing until fully incorporated.

In a separate bowl, whisk together the flour, oats, baking soda, and salt. Gradually mix into the wet ingredients until just combined.

Portion the dough onto the prepared baking sheets, leaving about 2 inches between each.

Bake for 9-11 minutes or until edges are set. Allow to cool for 5 minutes on the sheets before transferring to a wire rack for 30 minutes.

In a stand mixer, beat softened butter and powdered sugar until fluffy. Gradually add heavy cream, vanilla extract, and salt until smooth.

Once cookies are cool, pipe or spread vanilla cream onto the flat side of one cookie and top with another cookie to create a sandwich.