Preheat your oven to 325°F (163°C) and line two baking sheets with parchment paper.

In a stand mixer, beat the butter, brown sugar, and molasses together on medium speed for about 2 minutes until creamy.

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

Gradually add flour, oats, baking soda, and salt, mixing on low speed until just combined.

Scoop dough onto prepared baking sheets, spacing about 2 inches apart.

Bake for 9-11 minutes until edges are firm and centers remain soft.

Let cookies rest for 5 minutes on the baking sheet before transferring to a wire rack to cool completely.

Beat together the cream filling ingredients until creamy and fluffy.

Pipe about 2 tablespoons of the filling onto the bottom of one cookie and sandwich it with another cookie.

Store in an airtight container at room temperature for up to 5 days.