01 - Preheat the oven to 350°F. Line two baking sheets with parchment paper.
02 - In a large bowl, cream together butter, brown sugar, and granulated sugar until light and fluffy, about 2 minutes.
03 - Add eggs and vanilla extract. Beat until well combined.
04 - In a separate bowl, whisk together flour, baking soda, baking powder, salt, and cinnamon.
05 - Gradually add dry ingredients to the wet mixture, mixing just until incorporated.
06 - Fold in rolled oats with a spatula.
07 - Scoop tablespoon-sized portions of dough onto prepared baking sheets, spacing them about 2 inches apart.
08 - Bake for 10 to 12 minutes, or until cookies are just set and lightly golden around the edges.
09 - Let cookies cool on the baking sheets for 5 minutes, then transfer to a wire rack to cool completely.
10 - In a medium bowl, beat butter until creamy. Gradually add powdered sugar, cream, vanilla, and salt. Beat until light, fluffy, and spreadable.
11 - Pair cookies of similar size. Spread or pipe about 1 tablespoon of cream filling onto the flat side of one cookie and top with another to form a sandwich.
12 - Serve immediately or store in an airtight container.