Preheat oven to 350 degrees Fahrenheit and line baking sheets with parchment paper.
Stir the flour, cocoa powder, baking soda, and salt together.
Beat the sugar and butter together with an electric mixer until fluffy.
Add the eggs, vanilla, and peppermint, and beat on medium until just combined.
Slowly beat in the flour mixture.
Stir in the peppermint chunks. Use a medium-sized cookie scooper (it holds 1.5 tablespoons of liquid) to measure out the dough and place it on the prepared baking sheet. If desired, sprinkle some crushed candy canes on top of the dough before baking.
Bake 8 to 9 minutes. Cool for 3 minutes on the baking sheet and then transfer the cookies to cooling racks. The cookies will be very soft and puffy and will flatten as they cool.