Preheat your oven to 375F. Line two sheet pans with parchment paper.
Using a stand or hand mixer, cream together the butter and granulated sugar until light and fluffy— about 2 minutes on medium-high speed. Make sure to scrape down the sides of the bowl 1-2 times.
With the mixer on low, add the egg and vanilla extract. Mix until just combined, do not overmix.
Next, with the mixer on low, add the flour and cocoa powder. Mix until there are no large lumps of dry ingredients remaining.
Lastly, add the chocolate chunks and peppermint chips. Fold them into the dough with a silicone spatula.
Scoop the cookies onto the parchment-lined baking sheets.
Bake for 12-14 minutes, or until the cookies are set in the center. Ovens can vary widely so I highly recommend checking your cookies around the 8-minute mark to see how they are turning out.
Store the cookies in an airtight container at room temperate for up to 2 days.
Notes
Chocolate chips can be substituted for the chocolate chunks.
If you can't find white chocolate peppermint chips you can substitute ¼ cup white chocolate chips and ¼ cup crushed candy cane.
These cookies are best when served warm. I like to heat them for 15-20 seconds in the microwave for that “fresh from the oven” taste.