Preheat oven to 350°F (175°C).

In a bowl, whisk together flour, cocoa powder, baking soda, and salt.

In another bowl, cream butter, granulated sugar, and brown sugar until smooth.

Add egg and vanilla; mix well.

Gradually incorporate dry ingredients into the wet mixture.

Fold in chocolate chips and peppermint extract.

Drop tablespoon-sized balls onto lined baking sheets about two inches apart.

Bake for 10-12 minutes until edges are set but centers remain soft. Let cool slightly before serving.