Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper for easy cleanup.

In a medium bowl, whisk together the flour, rolled oats, baking soda, pumpkin pie spice, and salt. Set this mixture aside.

In a large mixing bowl, beat the softened butter and brown sugar together until light and fluffy—about 2-3 minutes.

Add the canned pumpkin, egg yolk, and vanilla extract. Mix until well combined.

Gradually add the dry ingredient mixture to the wet ingredients. Stir until just combined; the dough should be thick and slightly sticky.

Using a tablespoon or cookie scoop, drop rounds of the dough onto the prepared baking sheets, spacing them about 2 inches apart.

Bake for 12-15 minutes, or until the edges are golden and the cookies look set. Allow them to cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.

In a clean bowl, beat the softened butter until creamy. Gradually add the powdered sugar, followed by the marshmallow cream, vanilla extract, and a pinch of salt. Beat until fluffy and well combined.

Once the cookies are completely cooled, spread a generous layer of the filling on the flat side of one cookie. Top with another cookie, flat side down, to create a sandwich. Repeat until all cookies are filled.

These cream pies are best served fresh but can be stored for later. Enjoy your delicious creations!