01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a large bowl, cream together the butter, granulated sugar, and brown sugar until light and fluffy using an electric mixer.
03 - Beat in the eggs one at a time, then add vanilla and peppermint extracts until fully incorporated.
04 - In a separate bowl, whisk together flour, cocoa powder, baking soda, and salt until well blended.
05 - Gradually add the dry ingredients to the wet mixture, mixing until just combined. Do not overmix.
06 - Fold in the chocolate chips until evenly distributed throughout the dough.
07 - Drop tablespoon-sized balls of dough onto the prepared baking sheets, spacing them about 2 inches apart to allow for spreading.
08 - Bake for 9 to 11 minutes, until edges are set but centers remain slightly soft. Cool on the baking sheets for 5 minutes.
09 - Transfer cookies to a wire rack to cool completely before frosting.
10 - Beat the butter until creamy. Gradually add powdered sugar, then milk and peppermint extract. Mix until smooth and fluffy.
11 - Add green food coloring a few drops at a time, mixing until desired shade is reached.
12 - Once cookies are completely cool, spread or pipe frosting on top of each cookie.
13 - Allow frosting to set for about 15 minutes before serving or storing.