Preheat your oven to 350°F (175°C).

In a large bowl, cream together the softened butter, granulated sugar, and brown sugar until smooth.

Beat in the eggs one at a time, then stir in the vanilla extract.

In another bowl, whisk together the flour, cocoa powder, baking soda, and salt. Gradually mix the dry ingredients into the wet mixture until combined.

Fold in the chocolate chips and crushed peppermint candies.

Drop rounded tablespoons of dough onto ungreased baking sheets.

Bake for 10-12 minutes, or until the edges are set.

Let the cookies cool on the baking sheets for a few minutes before transferring them to wire racks to cool completely.

For the frosting, beat together the powdered sugar, milk, and peppermint extract until smooth.

Frost cooled cookies and sprinkle with additional crushed peppermint if desired.