Preheat the oven to 350°F (175°C). Line baking sheets with parchment paper.

In a large bowl, cream together the softened butter, brown sugar, and granulated sugar until smooth.

Beat in the eggs one at a time, then stir in the vanilla extract.

In another bowl, whisk together the flour, baking soda, and salt. Gradually add the dry ingredients to the wet mixture.

Fold in the oats until well combined.

Drop rounded tablespoons of dough onto the prepared baking sheets, spacing them about 2 inches apart.

Bake for 10-12 minutes, or until the edges are lightly golden. Allow to cool on the baking sheets for 5 minutes before transferring to a wire rack.

In a medium bowl, beat together the softened butter and powdered sugar until smooth and creamy.

Stir in the vanilla extract until well combined.

Once the cookies are completely cooled, spread a generous amount of the cream filling on the flat side of half of the cookies.

Top with the remaining cookies to form sandwiches.