In a medium mixing bowl, whisk together flour, cocoa, salt, and baking powder. Set aside. Using a hand mixer and a large mixing bowl, cream the butter and sugars until light and fluffy. Beat in the eggs one at a time until combined. Beat in chocolate and vanilla. Gradually add flour mixture until well combined. Shape dough into a disk. Wrap in plastic wrap in place in refrigerator for at least 1 hour.

In a large mixing bowl using a hand mixer, beat the butter, peppermint, and salt together. Using a low speed on the mixer, gradually add the confectioners' sugar and the milk. Frosting should be thick and fluffy. Add more confectioners' sugar if needed. At this point you can add a couple of drops of red food coloring to give the frosting a pink color. Refrigerate until ready to use. (Dough will be extremely hard when removed from the refrigerator, let it relax a few minutes.)

Preheat oven to 350 degrees F. On a lightly floured surface, roll out the dough to 1/8 inch thick. Using a 2-inch round cutter, cut out 36 rounds. Place the cookies spaced 1 inch apart on a parchment lined sheet tray and bake for 7-9 minutes. Keep unused dough in refrigerator while waiting to bake.

Let cookies cool completely. Place peppermint candies on a flat plate. Using a small off set spatula or butter knife, ice one cookie liberally with peppermint frosting making sure it goes all the way to the edges of the cookie. Place another cookie on top to make a sandwich. Roll the edges of the cookie sandwich in the peppermint candies and serve.

Serve with a large very cold glass of milk.