This cake is made with soft layers of dark chocolate cake filled with creamy peppermint buttercream, rich chocolate ganache, and crushed peppermint candies.
Preheat oven to 350 °F. Spray three 6-inch round cake pans or two 8-inch round cake pans with non-stick spray, line the bottom of each pan with parchment paper and spray again. Set aside.
In the stand mixer bowl fitted with a paddle attachment, stir together the all-purpose flour, granulated sugar, baking soda, and salt. Set aside.
Add the eggs and the vegetable oil on low until well incorporated.
Pour in the buttermilk and add brewed coffee. Mix on medium for 30 seconds. Scrape down the sides of the bowl.
Evenly distribute the cake batter among the three cake pans and bake for about 35-40 minutes or until a toothpick inserted into the center of each cake comes out clean or with just a few moist crumbs.
Remove cakes from oven and let cool in pans for 10 minutes before inverting onto cooling racks to cool completely — wrap cakes in plastic wrap and place in the freezer to chill for 30 minutes.
Add semi-sweet chocolate chips to a small microwavable bowl. In another small microwavable bowl, heat the heavy cream to a light simmer for about 1 minute.
Pour hot, heavy cream over chocolate chips. Allow chocolate to melt for 1 minute. Use a whisk or rubber spatula to mix the chocolate and cream. Mix until its velvety smooth. If chocolate is still not melted, heat in the microwave in 15-second increments.
In the stand mixer bowl fitted with the paddle attachment, beat the butter on high until light and fluffy, about 5 minutes.
Turn the mixer to low, gradually add powdered sugar, followed by the heavy cream. Then add peppermint extract, vanilla extract, and salt. Mix until incorporated completely. Scrape down sides of the bowl.
Turn the mixer to medium-high and beat the buttercream for about 5 minutes until light and fluffy. Scrape down sides of the bowl. Turn the mixer on low and mix for 2 minutes to push out any air bubbles.
Split the buttercream in half, leave one-half white and color the other half with super red gel food coloring.
Fill a piping bag fitted with #844 piping tip and 1/2 cup of white and 1/2 cup of red buttercream and set aside.
Remove the cake layers from the freezer and unwrap the cake layers. Next, use a serrated knife to cut off the dome of the cakes to make the layers flat and even.
Add a small amount of buttercream onto the center of the cake board. Layer the chilled dark chocolate cake, cut side up onto the cake board.
Then pipe a ring of red buttercream in the center followed by a ring of white buttercream. Continue to add a ring of red and white buttercream then use an offset spatula to smooth it.
Place another cake layer cut side down over the top. Repeat the process for another layer — Crumb coat the whole cake with white buttercream and freeze for 30 minutes.
Starting from the bottom, while spinning the cake, squeeze consistent pressure on the piping bag with white buttercream, pipe two rows.
Next pipe two rows of red buttercream followed by two more rows of white buttercream. Repeat until the sides are fully covered. Then pipe a single row of each buttercream on top of the cake.
Use a cake scraper to make the cake smooth on the top and sides. Use the offset spatula to add more buttercream to fill in any gaps. Repeat the process until the sides are smooth.
Add the chocolate ganache to a squeeze bottle and drip the ganache over the sides and on top. Then add crushed peppermint candies to the bottom of the cake.
Finally, pipe swirls on top of the cake with the piping bag filled with white and red buttercream. Sprinkle crushed peppermint candies on top of the cake. Serve the cake at room temperature.