Preheat your oven to 350°F (175°C).
In a large bowl, use a hand mixer or stand mixer to cream the room temperature butter with the brown sugar, granulated sugar, and cocoa powder until light and fluffy.
Beat in the egg, vanilla extract, and peppermint extract until well combined.
In a separate medium bowl, whisk together the all-purpose flour, baking soda, and salt.
Gradually add the dry to the wet , mixing on low speed until just combined. Be careful not to overmix.
Stir in the semisweet chocolate chips by hand using a spatula.
Drop rounded teaspoonfuls of dough onto an ungreased baking sheet, placing them about 2 inches apart.
Bake for 10–12 minutes. The edges should be set, but the centers will still be slightly soft.
Let them cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely.
Do not overmix the dough after adding the flour.
Mix only until the flour is just incorporated to ensure a tender, soft cookie.
