Preheat oven to 350 degrees F. Line 2 baking sheets with parchment paper.
In a large bowl whisk together flour, baking soda and salt; set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream butter, and sugars until combined. Reduce speed to low and add egg, vanilla and peppermint extract; mix until combined. Add flour mixture; mix until just combined. Stir in chocolate chips and Thin Mint Cookies until just combined.
Drop by rounded tablespoons of dough onto parchment-lined baking sheets spacing 1 1/2-inches between each. Bake cookies until edges have just begun to set but centers are still very soft, 8-10 minutes.
Let cool on baking sheet for 3 minutes before transferring to cooling rack.