Preheat oven to 350°F.
Place butter in a stand mixer, fitted with a paddle attachment (or use a hand mixer) and beat for about 3 minutes or until light and fluffy. Add sugar and cream together.
Add mint and vanilla, mix and scrape down the sides of the bowl.
In another bowl combine the flour, cocoa powder and salt. With the mixer on low, begin adding the flour mixture. Add until all flour has been used and the mixture just comes together and forms cookie dough. Wrap cookie dough into a disc and chill for at least 30 minutes.
Very lightly flour a clean surface and roll your dough out until 1/8 inch thick.
Cut out 1 ½” circles in the dough. Place cookies onto a parchment lined baking sheet and chill in the refrigerator for 30 minutes.
Bake cookies for 18 to 20 minutes or until the cookies have baked through. Transfer cookies to a cooling rack and allow cooling completely (repeat until all cookie have been baked). To assemble: Carefully dip each cookie into the melted chocolate, shaking off any excess and placing them onto a parchment lined baking sheet. Allow thin mints to sit until the chocolate has fully set, about an hour. Remove from the parchment and serve. These cookies will keep in an airtight container for 3 to 5 days.