Preheat oven to 350°F. Line a 9x13-inch baking pan with parchment paper and lightly spray it with nonstick spray. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat the butter, sugar, and brown sugar together on high speed until smooth and creamy, about 1 minute.
1 cup unsalted butter, 1⅓ cups granulated sugar, ⅓ cup brown sugar
Add in the egg yolks. Beat together for 30 seconds to incorporate. Add in the egg whites, peppermint extract, salt, and vanilla and mix to combine.
5 large eggs, 1 egg white, 1½ teaspoons peppermint extract, ¾ teaspoon kosher salt, ½ teaspoon pure vanilla extract
Melt the dark chocolate in 30-second intervals in the microwave. Mix it into the stand mixer bowl.
14 ounces chopped dark chocolate
Add in the cocoa and mix to incorporate. Add in the hot coffee and stir. Lastly, add in the flour and mix until fully incorporated.
6 tablespoons unsweetened cocoa powder, ¼ cup strong coffee, 1⅔ cups all-purpose flour
Pour the batter into the prepared baking pan and place into the preheated oven to bake for 50 minutes, or until a toothpick inserted comes out clean or with moist crumbs. Remove from the oven and place onto a cooling rack to cool to room temperature.
Once the brownies are cooled, make the topping. Heat the heavy cream in a heat-proof bowl in 30-second increments, stirring in between. Pour the heated heavy cream over the chocolate chips and let them set for 1 minute. Mix the chocolate chips and heavy cream until smooth and creamy. Pour the ganache onto the brownies and spread to the edges. Sprinkle the crushed candy canes over the surface of the ganache.
¾ cup dark chocolate chips, ⅓ cup heavy cream, ½ cup crushed candy canes
Place the brownies into the refrigerator for 10 minutes to let the ganache set. Slice and serve.