01 - Preheat 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 wet mixture, mixing just until incorporated. Fold in rolled oats with a spatula.
06 - Scoop tablespoon-sized portions onto prepared baking sheets, spacing 2 inches apart. Bake for 10-12 minutes until just set and lightly golden around edges.
07 - Let cookies cool on baking sheets for 5 minutes, then transfer to wire rack to cool completely.
08 - Beat butter until creamy. Gradually add powdered sugar, cream, vanilla, and salt. Beat until light, fluffy, and spreadable.
09 - Pair cookies of similar size. Spread about 1 tablespoon cream filling onto flat side of one cookie and top with another to form sandwich.