01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a medium bowl, whisk together flour, cocoa powder, baking soda, salt, and espresso powder until evenly mixed.
03 - In a large bowl, beat softened butter with granulated and brown sugars until creamy and light, about 2 minutes.
04 - Add the egg, vanilla extract, and peppermint extract to the butter mixture and beat until fully combined.
05 - Gradually add the dry mixture to the wet ingredients, stirring just until incorporated without overmixing.
06 - Gently fold in semisweet chocolate chunks and half of the crushed peppermint candies.
07 - Scoop tablespoon-sized portions of dough onto prepared baking sheets, spacing them about 2 inches apart.
08 - Bake for 9 to 11 minutes until edges are set but centers remain slightly soft.
09 - Remove from oven and immediately sprinkle with remaining crushed peppermint candies. Let cool on sheets for 5 minutes, then transfer to wire racks.
10 - Once completely cooled, drizzle melted white chocolate over cookies if desired and allow to set before serving or storing.