01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - Beat butter, granulated sugar, and brown sugar in a large bowl until light and fluffy.
03 - Add eggs, vanilla extract, and peppermint extract. Beat until fully combined.
04 - Whisk together flour, cocoa powder, baking soda, and salt in a separate bowl.
05 - Gradually add dry ingredients to wet mixture, mixing just until incorporated.
06 - Fold semisweet chocolate chips into the dough.
07 - Scoop tablespoon-sized dough balls onto prepared baking sheets, spacing 2 inches apart.
08 - Bake for 9-11 minutes until edges are set but centers remain soft.
09 - Let cool on baking sheets for 5 minutes, then transfer to wire rack to cool completely.
10 - Beat butter until creamy. Gradually add powdered sugar, milk, and peppermint extract, beating until smooth and fluffy.
11 - Add green food coloring and mix until desired color is achieved.
12 - Spread or pipe green mint frosting onto completely cooled cookies.