In a large bowl, whisk together the flour, cocoa powder, baking soda, and salt.
In a large mixer bowl, beat the butter, brown sugar, and white sugar until fluffy, about 5 to 10 minutes.
Add the eggs, one at a time, beating until well blended after each addition. Add in the vanilla.
Slowly add the flour mixture, scraping down the sides as needed.
Fold the chocolate chips and crushed peppermint into the batter.
Using a small cookie scoop, drop the cookies onto the prepared baking sheet about 2 inches apart.
Bake for 8 to 10 minutes. Allow the cookies to cool for 5 to 7 minutes on the baking sheet before transferring to a wire rack to cool completely.