01 - Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper.
02 - In a large bowl, cream together butter, brown sugar, and granulated sugar until light and fluffy, approximately 2 minutes.
03 - Add eggs and vanilla extract; beat until thoroughly incorporated.
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. Fold in rolled oats with a spatula.
06 - Scoop tablespoon-sized portions of dough onto prepared baking sheets, spacing them 2 inches apart. Bake for 10 to 12 minutes, until cookies are just set and lightly golden around the edges.
07 - Let cookies cool on the baking sheets for 5 minutes, then transfer to a wire rack to cool completely.
08 - In a medium bowl, 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 or pipe approximately 1 tablespoon of cream filling onto the flat side of one cookie and top with another to form a sandwich.