Weigh out ingredients
You'll need all-purpose flour, cocoa powder, salt, butter, baking powder, sugar, egg yolk, milk, and vanilla extract.
Make the dough
Whisk together the flour, baking powder, cocoa powder, and salt. In a separate bowl, beat the butter and sugar for 1-2 minutes. Beat in the egg, milk, and vanilla. Add in the dry ingredients. Mix until just combined.
Chill & Shape
Shape the dough into a disk and refrigerate for 1 hour or overnight. On a lightly floured surface, roll out the cookie dough to about ¼" thick and cut out 2-inch circles andfor about 10 minutes. Repeat until all of the dough is used.
Bake the cookies for about 10 minutes at 350 degrees. Allow to cool completely.
Assemble & enjoy!
Pair the cookies up, pipe chocolate ganache on the bottom cookie, and press the paired cookie on top. Chill the sandwiched cookies in the fridge for a few minutes. Dip each sandwich cookie in the melted chocolate then top with crushed candy cane pieces.