http://www.runs-with-spatulas.com/2012/04/thin-mint-cookies.html

Thin Mint Cookies
Adapted from: my Katrina's Kitchen

1 cup butter, at room temperature
1 cup powdered sugar
1 teaspoon vanilla extract
1/2 cup unsweetened cocoa powder
1/2 cup dutch-processed cocoa powder
3/4 teaspoon salt
1 1/2 cups all-purpose flour

14 ounces mint-flavored dark chocolate candy melts

The the large bowl of a mixer, cream the butter until light and fluffy. Slowly add in the powdered sugar, mixing on low until just combined. Increase the mixer speed and continue to cream until well blended. Stir in the vanilla, salt, and both cocoa powders. Add the flour, 1/2 cup at a time until fully incorporated. Mixture may be on the crumbly side.

Turn dough out onto a clean work surface, kneading together until smooth. Separate dough into 2 portions, flattening each into a disk. Wrap in plastic wrap and chill for 10 minutes.

Preheat oven to 350 degrees F. Line two baking pans with parchment paper and set aside.

Remove one of the chilled dough disks from the fridge. Lightly dust counter with flour and roll dough out to about 1/8-inch thickness. Cut out cookies and transfer to a prepared baking sheet. Repeat with remaining dough until baking pan is full. Bake for 10 minutes. Allow cookies to cool on pan for 5-10 minutes, then transfer to a wire rack to cool completely.

While cookies are baking, prepare chocolate coating. Heat the chocolate melts in a small bowl according to package instructions. Stir every 20-30 seconds until chocolate becomes smooth. Dip each cooled cookie in the chocolate face down, then flip right-side up and remove from bowl, shaking any excess chocolate off (a fork works great here). Place on a wax paper covered baking sheet to set. Once the sheet is full place in fridge for about a 1/2 hour to finish setting the chocolate.

Makes: about 3 dozen cookies (serving size: 1 cookie)