• Line a baking sheet with a piece of parchment paper.
• In a medium mixing bowl, add the butter, brown sugar, and granulated sugar. Use a hand mixer (or stand mixer) and beat on medium-high speed until light and creamy - at least 3 minutes. Add the egg yolk and vanilla and mix until well combined. Scrape the sides of the bowl as needed.
  6 tablespoons unsalted butter, room temperature, 6 tablespoons brown sugar, light or dark, 1 large egg yolk, 1/2 teaspoon vanilla extract, 2 tablespoons granulated sugar
• Sprinkle the flour, cocoa powder, baking powder, and salt over the butter mix. On medium-low speed, mix until a thick dough forms. It will start off crumbly, then the butter will moisten the flour, and the dough will start to pull away from the sides of the bowl. Note - If a dough ball doesn't come together, add a teaspoon of milk at a time until it does.
  3/4 cup all-purpose flour, 3.5 tablespoons unsweetened cocoa powder, Dutch process, 1/4 teaspoon baking powder, 1/4 teaspoon salt
• Use a cookie scoop to portion the cookies. Roll the dough into a ball in the palm of your hands and place at least 2 inches apart on the baking sheet. At this point, you can roll the dough balls through granulated sugar. Using the back of a teaspoon, make wells in the center of each cookie.
• Cover the baking sheet with plastic wrap and refrigerate for at least 30 minutes.
• Preheat the oven to 350F degrees and adjust the oven rack to the middle position.
• Bake the cookies for 10 to 12 minutes, or until the edges are set. While baking, the wells may fill back in slightly. As soon as the cookies come out of the oven, place the baking sheet on a wire cooling rack and reform the wells with the back of the teaspoon. Let the cookies cool on the pan for 10 minutes, then transfer to the wire rack to cool completely. Note - The cookies may crack a little around the edges when baked, which is ok. You can try to press the cracks back together as soon as they come out of the oven, or just leave them.

Peppermint Ganache Filling

• Once the cookies have cooled, make the ganache. Add the chocolate chips to a small mixing bowl. Then, warm the heavy cream in the microwave or on the stove-top. Heat until warm, not boiling.
  1/4 cup semi-sweet chocolate, 3 tablespoons heavy whipping cream
• Pour the warm cream over the chocolate and let the mix sit for about 3 minutes to allow the cream to melt the chocolate. Stir the ganache until fully mixed and smooth. Add the peppermint and taste - add a little more if you prefer a stronger peppermint flavor. Let the ganache cool and start to thicken for about 10 minutes.
  1/8 teaspoon peppermint extract
• Pour or pipe the ganache into the wells of the cookies and sprinkle with crushed candy canes.
  crushed candy canes