Combine flour, cocoa, and salt in a bowl, whisk together and set aside.
In a stand mixer, beat together butter and sugar until light and fluffy about 3 minutes.
Blend in egg, peppermint extract and vanilla.
Add in the dry ingredients in small increments, mixing until just incorporated on low speed. Continue until all dry ingredients are added and no streaks remain.
Form the dough into a disc and wrap well with plastic wrap. Refrigerate for 1-2 hours.
Preheat oven to 325°F. Line baking sheets with silicone baking mats or parchment paper.
Roll dough out on a floured flat surface to about ¼ inch thickness. Cut out 3 inch rounds using a cookie cutter or a small water glass.
Place cut outs on the prepared baking sheets about one inch apart. Bake 10-11 minutes.
Allow to cool on baking sheet for 5 minutes, then transfer to a cooling rack to cool completely.
Using a double boiler, heat dark chocolate until melted.
Prepare two cookie sheets with wax paper.
Dip cooled cookies into melted chocolate, ensuring both sides are well coated. Allow excess chocolate to drip off. Place on prepared cookie sheets. Repeat until all cookies are coated. Chill in the refrigerator for 15 minutes until chocolate is set.
Put remaining melted chocolate into a resealable plastic bag. Snip a small corner and drizzle on cookies in a zigzag pattern. Allow to set.
Store in an airtight container at room temperature.
