For the cake:
- 10 ounces (283 grams) bittersweet chocolate, finely chopped
- 2/3 cup (57 grams) Dutch-process cocoa, sifted
- 2 teaspoons instant espresso powder
- 1 cup boiling water
- 1 3/4 (222 grams) cups all-purpose flour
- 1 cup (200 grams) granulated sugar
- 3/4 cup (150 grams) packed light brown sugar
- 1 teaspoon salt
- 1 teaspoon baking soda
- 1 cup (227 grams) sour cream, at room temperature
- 1/2 cup vegetable oil
- 4 large eggs, at room temperature
- 2 large egg yolks, at room temperature
- 1 tablespoon white vinegar
- 2 teaspoons vanilla extract
For the buttercream:
- 4 sticks (452 grams) unsalted butter, at room temperature
- 5 cups (625 grams) powdered sugar (preferably organic with tapioca starch instead of cornstarch)
- 1/4 cup milk or heavy cream
- 2 teaspoons vanilla extract
- 1/2 teaspoon fine salt
- 1/2 teaspoon peppermint extract
For the chocolate drip:
- 2 1/2 ounces (75 grams) semisweet or bittersweet chocolate, finely chopped
- 2 1/2 ounces (75 grams) heavy cream
- Crushed candy canes*
Make the cake:
Preheat the oven to 350°F. Butter and flour two 8-inch round cake pans.
In a large heatproof bowl, add the chocolate, cocoa powder, and espresso powder. Pour boiling water over mixture. Cover and let stand for 5 minutes. Whisk mixture gently until smooth then set aside to cool completely.
In a medium bowl, whisk together the flour, sugars, salt, and baking soda.
Whisk sour cream, oil, eggs, yolks, vinegar, and vanilla into the cooled chocolate mixture until smooth. Stir in the flour mixture until smooth, being careful not to overmix.
Divide the batter evenly between the prepared pans and bake for 35 to 40 minutes, or until a cake tester comes out clean. Cool in the pans for 30 minutes, then carefully turn them out onto a cooling rack to cool completely. Refrigerate to chill before assembling and frosting.
Make the buttercream:
In the bowl of a stand mixer fitted with the paddle attachment, beat together the sugar and butter. Continue beating on medium speed until well blended and then increase the speed to medium high and beat for another 3 minutes. Scrape down the bowl before adding the milk or cream, vanilla, salt, and peppermint and beat on medium high for 1 minute, adding more cream or more powdered sugar if needed to achieve desired consistency.
Place one cake layer on a cake stand or serving plate. Frost the top of the cake generously, as this will become the filling. Top with the other cake layer, flat side up.
With an offset spatula, spread a very thin layer of frosting all over the cake. This layer is a crumb coat and should act like spackle. For the smoothest frosting, return the cake to the fridge or freezer until firm to the touch. Spread the remaining frosting all over the cake. If desired, focus the frosting on the top to maintain the ‘naked’ look.
Refrigerate while you prepare chocolate drip.
Make chocolate drip:
Place the chopped chocolate in a heatproof bowl. Bring the heavy cream to a simmer, then immediately remove from heat and pour over chocolate. You can also do this in the microwave. Cover for a few minutes then stir until smooth.
Allow to cool until it has thickened but is still pourable, about 10 minutes. Don’t place ganache in the fridge to cool. Test the consistency of the drip by pouring down the side of a glass. If it’s too thick, microwave for 5 to 10 seconds. If it’s too thin, allow to continue to cool. Spread the drip all over the top of the cake and allow it to drip slowly down the sides. Sprinkle crushed candy canes in a border around the diameter of the top of the cake before the drip sets.
The cake can be stored, covered, at room temperature for up to 1 day or in the fridge for up to 3 days. Note that candy canes will bleed into the chocolate drip and frosting, so this cake is best served the day it’s decorated.