01 - Preheat the oven to 350°F. Line two baking sheets with parchment paper.
02 - In a medium bowl, whisk together flour, baking soda, and salt. Set aside.
03 - In a large bowl, beat the softened butter, granulated sugar, and brown sugar with an electric mixer until light and fluffy, about 2-3 minutes.
04 - Add eggs, one at a time, beating well after each addition. Mix in peppermint extract, vanilla extract, and green food coloring until evenly colored.
05 - Gradually add the dry ingredients to the wet mixture, mixing on low speed just until combined.
06 - Fold in chocolate chips and chopped dark chocolate, if using.
07 - Scoop tablespoon-sized portions of dough onto prepared baking sheets, spacing them about 2 inches apart.
08 - Bake for 9-11 minutes, or until edges are set but centers are still soft.
09 - Cool on the baking sheets for 5 minutes, then transfer to a wire rack to cool completely.