Preheat the oven to 350°F (175°C).

In a mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy.

Add the eggs one at a time, mixing well after each addition, 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 ingredients, mixing until just combined.

Fold in the oats until evenly distributed.

Drop rounded tablespoons of dough onto a baking sheet lined with parchment paper.

Bake for 12-15 minutes or until the edges are golden brown. Let cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely.

In a mixing bowl, beat together the vegetable shortening, powdered sugar, and vanilla extract until smooth and creamy.

Once the cookies are completely cool, spread a generous amount of cream filling on the flat side of one cookie and top with another cookie to create a sandwich.