In a medium bowl, sift together flour, cocoa powder, baking powder, baking soda, and salt. Set aside.
In a large bowl, combine butter, granulated sugar, and brown sugar; cream together until mixture appears light and fluffy. Add egg and milk; beat until thoroughly mixed. Add flour mixture; stir until well mixed. Press dough into a ball, cover and refrigerate until well chilled, at least 2 hours.
When ready to bake preheat oven to 375 degrees F. Lightly grease Cookie Sheets or line with Silicone Baking Mats.
On a lightly floured surface, and using a lightly-floured Rolling Pin, roll the dough to a 1/8-inch thickness. Cut dough into desired shapes using your favorite Cookie Cutters that has been dipped in flour (to help prevent dough from sticking to the cutter).
Place cutout dough 2-inches apart on baking sheets. Always leave room between cookies on the cookie sheets. If the cookies are extremely large cookies or the recipe calls for more space, adjust the space
Bake approximately 6 minutes or until cookies are set. Remove cookies from baking sheets and cool on wire cooling racks.
Prepare Peppermint Filling. Spread a small amount of filling on a cookie. Top with another cookie to make a sandwich. Continue with the remaining cookies. Set cookies aside until filling is set.
In a medium-size bowl, combine confectioners sugar, half and half cream, peppermint extract, and salt. Add food coloring if desired.
Chocolate Mint Wafer Cookies Recipe: https://whatscookingamerica.net/Cookie/ChocolateMintWafers.htm