Preheat your oven to 350°F (175°C). Line baking sheets with parchment paper or silicone mats.

In a medium bowl whisk together flour, cocoa powder (if using), baking powder, and salt. Set aside.

In a large mixing bowl, beat the room-temperature butter with the granulated and brown sugars until light and fluffy, about 2–3 minutes. Scrape down the sides as needed.

Beat in the egg and vanilla extract until incorporated. If using peppermint extract, add it here but use sparingly.

Gradually add the dry ingredients to the wet, mixing until just combined. If using nuts, fold them in now.

For an extra-tender crumb, chill the dough for 15–30 minutes.

Use a cookie scoop or tablespoon to portion dough (about 1–1.5 tablespoons each). Roll into smooth balls and space them 2 inches apart on the prepared baking sheets.

Use your thumb or the back of a small spoon to gently press an indentation into each dough ball. Bake for 10–12 minutes.

For chocolate ganache: heat the heavy cream until steaming and then pour over chocolate chips in a heatproof bowl. Let sit 1 minute, then stir until smooth.

Spoon or pipe the warm ganache into the cooled cookie indentations. Immediately sprinkle crushed candy canes over the filled centers so they adhere.

Transfer cookies to a cooling rack and allow ganache to set fully (about 30–45 minutes).