Heat the oven to 375F. Line two baking sheets with parchment paper.
In a large mixing bowl, cream the butter and sugars together until fluffy and pale. Add in the eggs one at a time, fully mixing after each. Add the peppermint oil and mix to combine.
Sift in the flour, cocoa powder, baking powder, baking soda, and salt. Stir to partially combine.
Add the chopped chocolate and candy cane. Stir to fully combine everything. I use my hands to complete the mixing process to make sure I get all the flour.
Scoop the dough in very heaped Tbsps, and roll them into balls. Place on the baking sheet and flatten slightly.
Bake for 6 minutes, then rotate and bake for another 6 minutes. You want to slightly under bake these cookies, so that they maintain their soft centers. Sprinkle the tops of each cookie with more candy cane immediately when they come out of the oven.
Allow to cool on their trays slightly, then transfer to a wire rack and cool fully before storing. Store in an airtight container for up to 3 weeks.