Creating your own Oatmeal Cream Pies can be a fun and rewarding experience. Follow these simple steps:

1. Preheat the Oven: Preheat your oven to 350°F (175°C). Line baking sheets with parchment paper.
2. Cream Butter and Sugars: In a large bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy.
3. Add Eggs and Vanilla: Beat in the eggs one at a time, then add the vanilla extract, mixing well.
4. Combine Dry Ingredients: In a separate bowl, whisk together the flour, baking soda, cinnamon, and salt.
5. Mix Oats: Gradually add the dry ingredients to the wet mixture, stirring until combined. Then, fold in the rolled oats until evenly distributed.
6. Scoop Dough: Drop rounded tablespoons of dough onto the prepared baking sheets, spacing them about 2 inches apart.
7. Bake: Bake in the preheated oven for 10-12 minutes, or until the edges are golden brown. The centers will look slightly underbaked.
8. Cool: Remove from the oven and allow the cookies to cool on the baking sheet for 5 minutes before transferring them to wire racks to cool completely.
9. Make Filling: In a medium bowl, mix together the marshmallow fluff and powdered sugar until smooth and creamy.
10. Assemble: Once the cookies are completely cool, spread a generous amount of the filling on the flat side of one cookie, then top with another cookie, pressing down gently.