01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a large bowl, beat softened butter and granulated sugar until light and fluffy, approximately 2-3 minutes.
03 - Beat in egg, vanilla extract, and peppermint extract until thoroughly combined.
04 - In a separate bowl, whisk together flour, cocoa powder, baking soda, and salt.
05 - Gradually add dry ingredients to wet ingredients, mixing until just combined. Do not overmix.
06 - Fold in semi-sweet chocolate chips until evenly distributed.
07 - Drop rounded tablespoons of dough onto prepared baking sheets, spacing 2 inches apart.
08 - Bake for 9-11 minutes until edges are set. Cool on baking sheet for 5 minutes before transferring to wire rack.
09 - Beat softened butter until creamy. Gradually incorporate powdered sugar, mixing well after each addition.
10 - Add milk, peppermint extract, and green food coloring. Beat until smooth and fluffy. Adjust color intensity as desired.
11 - Once completely cooled, spread or pipe green frosting onto each cookie.