Preheat your oven to 350°F and line a baking sheet with parchment paper.

In a stand mixer, beat the butter, brown sugar, and granulated sugar on medium-high speed for 2 minutes until light and fluffy.

Add in the eggs and vanilla extract. Beat again until smooth and fully combined.

In a separate bowl, whisk together the flour, baking powder, cinnamon, salt, and cornstarch.

Slowly add the dry ingredients into the wet ingredients, mixing on low until just combined.

Fold in the oats, chocolate chips, and mini chocolate chips using a spatula.

Scoop into evenly sized cookies and place on the baking sheet.

Bake for 11 to 13 minutes until the edges are set and the centers are still soft.

If needed, use a round glass or bowl to reshape the cookies while warm.

Let cool completely on a wire rack.

Beat the butter for 2 minutes until smooth and creamy.

Add vanilla extract.

Slowly mix in powdered sugar, starting on low and increasing speed.

Add heavy cream one tablespoon at a time until you reach your desired consistency.

Match cookies into pairs of similar size.

Pipe or spread buttercream onto the bottom of one cookie.

Add a drizzle or spoonful of salted caramel on top.

Place the second cookie on top and gently press.

Repeat until all cookies are assembled.