Preheat oven to 375°F. In a bowl, briefly whisk together the flour, cocoa powder, baking soda, and salt. Set aside.
In the bowl of a standing mixer or in a bowl with an electric hand mixer, blend together the butter and sugar until fluffy.
Blend in the egg yolk, vanilla, and 1/2 teaspoon of peppermint extract.
Gradually mix in the dry ingredients.
Scrape the dough into a zip-top bag and refrigerate for an hour.
When chilled, roll out the dough 1/4-inch thick on a floured surface. Cut out desired shapes. Here, I cut out cookie sticks using a dough scraper (or knife) 1/2-inch wide by 4-inches long.
Place on a parchment paper lined baking tray and bake until set and edges begin to brown, 10 to 12 minutes.
In a microwave-safe bowl, place the chocolate chips and shortening. Heat for 90 seconds at 70 percent power. Stir the chocolate and use the residual heat to fully melt the chocolate. If necessary, microwave at additional 15 second intervals. Stir in the remaining 1/2 teaspoon of peppermint extract.
When the chocolate cools a bit, transfer to a disposable decorating bag. Snip the tip and pipe chocolate on the cookies. Let set at room temperature or in the refrigerator.