01 - Preheat oven to 350°F. Line two baking sheets with parchment paper for easy cleanup and to prevent sticking.
02 - In a large bowl, beat softened butter, brown sugar, and granulated sugar together until light and fluffy, approximately 2 minutes.
03 - Add eggs and vanilla extract to the butter mixture. Beat until thoroughly combined and smooth.
04 - In a separate bowl, whisk together flour, baking soda, baking powder, salt, and ground cinnamon until evenly distributed.
05 - Gradually add the dry ingredient mixture to the wet ingredients, mixing just until incorporated. Avoid overmixing to prevent tough cookies.
06 - Fold in the rolled oats using a spatula until evenly distributed throughout the dough.
07 - Drop tablespoon-sized portions of dough onto prepared baking sheets, leaving approximately 2 inches of space between each to allow for spreading.
08 - Bake for 10 to 12 minutes, or until cookies are set and lightly golden around the edges while still slightly soft in the center.
09 - Allow cookies to rest on baking sheets for 5 minutes, then transfer to a wire rack to cool completely before filling.
10 - Beat softened butter in a medium bowl until creamy. Gradually add powdered sugar, heavy cream, vanilla, and salt. Continue beating until light, fluffy, and spreadable.
11 - Match cookies of similar size. Spread approximately 1 tablespoon of cream filling onto the flat side of one cookie and press another cookie on top to form a sandwich.
12 - Serve immediately for optimal texture, or store in an airtight container at room temperature for up to 3 days.