01 - Preheat oven to 350°F and 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.
03 - Beat in the eggs one at a time, then mix in vanilla and peppermint extracts.
04 - In a separate bowl, whisk together flour, cocoa powder, baking soda, and salt.
05 - Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Fold in chocolate chips.
06 - Drop tablespoon-sized balls of dough onto prepared baking sheets, spacing 2 inches apart.
07 - Bake for 8 to 10 minutes or until cookies are set but still soft in the center. Cool on baking sheets for 5 minutes, then transfer to a wire rack to cool completely.
08 - Beat the butter until creamy. Gradually add powdered sugar, milk, peppermint extract, food coloring, and salt. Beat until smooth and fluffy. Adjust the green color as desired.
09 - Once cookies are completely cool, spread or pipe green frosting on top of each cookie.
10 - Allow frosting to set before serving.