Step 1: Prepare the Dough

1. Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.

2. In a large mixing bowl, beat the butter, brown sugar, and granulated sugar together until light and fluffy.

3. Add the eggs and vanilla extract, then continue mixing until fully combined.

Step 2: Mix the Dry Ingredients

4. In a separate bowl, whisk together the flour, baking soda, salt, and cinnamon.

5. Gradually add the dry ingredients to the wet ingredients, mixing just until combined.

6. Stir in the rolled oats until evenly distributed in the dough.

Step 3: Bake the Cookies

7. Scoop tablespoon-sized portions of dough onto the prepared baking sheets, spacing them about 2 inches apart.

8. Bake for 10-12 minutes or until the edges are golden brown and the centers are slightly soft.

9. Let the cookies cool on the baking sheet for 5 minutes before transferring them to a cooling rack.

Step 4: Make the Cream Filling

10. In a medium bowl, beat the butter until smooth.

11. Add the powdered sugar, vanilla extract, and heavy cream, then mix until light and fluffy.

12. For extra fluffiness, mix in the marshmallow fluff.

Step 5: Assemble the Oatmeal Cream Pies

13. Transfer the filling to a piping bag or zip-top bag with the corner cut off.

14. Pipe a generous amount of filling onto the flat side of one cookie.

15. Place a second cookie on top, pressing lightly to sandwich them together.

16. Repeat with the remaining cookies and filling.