Glam Rock Layer Cake
Super dark, moist and buttery chocolate cake layers filled with colourful vanilla frosting and covered in a decadent jet-black glossy fudge frosting. And let's not forget the sprinkles!
Ingredients
For the "Black" Dark Chocolate Butter Cake layers:
  • 2 1/3 cups 315 g all-purpose flour
  • 3/4 cup plus one tablespoon 100 g best-quality black cocoa powder
  • 1 1 /2 teaspoons baking powder
  • 3/4 teaspoon salt
  • 1 1/2 cups 360 ml buttermilk, room temperature
  • 1/2 cup 120 ml hot coffee OR very hot water
  • 1 cup 227 g unsalted butter, room temperature
  • 2 1/2 cups 560 g packed light brown sugar
  • 2 teaspoons pure vanilla extract
  • 4 large eggs room temperature
  • 1/4 cup 60 g mayonnaise, room temperature
  • 1 1/2 teaspoons baking soda
  • 1 teaspoon distilled white vinegar
For the (purple frosting) Vanilla Frosting:
  • 1 cup 227 g unsalted butter, room temperature
  • 3 cups 375 g confectioners' sugar, sifted
  • 1/4 cup 60 ml whipping cream (heavy cream) or milk
  • 2 tablespoons water plus more if needed
  • 2 teaspoons pure vanilla extract
  • Pinch of salt
  • Few drops each AmeriColor Soft Gel Paste Color in Electric Purple and Regal Purple
For the Glossy Black Fudge Frosting:
  • 2 cups 454 g unsalted butter, softened
  • 4 cups 500 g confectioners' sugar
  • 3/4 cup 90 g premium dark (preferably black) cocoa powder (I used Guittard Noir)
  • 1/2 cup 120 ml hot water
  • 1/2 cup 120 ml sour cream
  • 1 1/2 teaspoons pure vanilla extract I used Nielsen-Massey
  • Generous pinch of salt
  • 8 ounces 240 g premium dark (but not extra dark) chocolate, chopped or chips, melted (I used Callebaut Callets)
  • Soft gel paste color in Super Black (or other concentrated black gel color of your choice, but this one is the only I can promise works for black coloring)
  • Sprinkles of your choice 1-2 cups, depending on size of the sprinkles
  • You will also need:
  • 1 large pastry bag disposable or reusable
  • Large plain round pastry tip I use Ateco #809
  • Sprinkles of your choice 1-2 cups, depending on size of the sprinkles--see Sweetapolita's Notes
Instructions
For the "Black" Dark Chocolate Butter Cake layers:
  1. Preheat the oven to 350F (180C). Spray two 7"x2" round cake pans (to be used twice for 4 layers) with baking spray (such as Pam for Baking), or grease the bottoms and add parchment rounds to each.
  2. In a large bowl or atop a large piece of parchment paper, sift together the flour, cocoa powder, baking powder and salt. In a large measuring glass with a spout, mix together the buttermilk and coffee/water. Set aside.
  3. In the bowl of an electric mixer fitted with the paddle attachment, or using a handheld mixer, beat the butter and brown sugar on medium speed until very light and fluffy, about 8 minutes. Add the vanilla and beat well. Add the eggs one at a time, mixing well (about 30 seconds) and scraping the sides of the bowl with a rubber spatula after each addition.
  4. Lower the speed to the lowest setting and add one third of the dry mixture until just combined, and add half of the buttermilk mixture. Repeat with the remaining flour and buttermilk mixtures. Remove the bowl from the stand mixer, and whisk in the mayonnaise.
  5. In a small bowl combine the baking soda and vinegar, and quickly add to the batter. Whisk until smooth, about 30 seconds. Divide one-quarter of the batter into each pan (this should weigh about 430 grams if you are using a digital scale).
  6. Bake the first two layers in the center of the oven until a wooden pick comes out with a few crumbs, 24-27 minutes. Let the cake layers cool on a wire rack for 10 minutes, and then gently invert onto the wire rack. Wipe the pans clean and repeat with the final layers. Let all of the layers cool completely. The cake layers will keep wrapped tightly in plastic wrap at room temperature for up to 3 days.
For the (purple filling) Vanilla Frosting:
  1. In the bowl of an electric mixer fitted with the paddle attachment, beat the butter on medium speed until very pale and creamy, about 8 minutes. Reduce the speed to low, and gradually add the confectioners' sugar, heavy cream, vanilla and salt. Beat for 1 minute.
  2. Increase the speed to medium-high and beat until very light and fluffy, about 6 minutes. Add a few drops of each AmeriColor Regal Purple and Electric Purple until desired shade is achieved. Frosting with keep in an airtight container in the refrigerator for up to 3 days. Bring chilled frosting to room temperature and beat on low speed to soften. If necessary, you can warm the frosting in a heatproof container in the microwave in 10-second intervals, stirring after each one, until smooth and spreadable.
For the Glossy Black Fudge Frosting:
If you have a food processor:
  1. Add all of the ingredients, except the melted chocolate and black food color, into the food processor, and pulse until everything is incorporated. Add the melted chocolate and pulse until smooth. Add a small amount of the black color (about 1/2 teaspoon). Pulse until combined. Let sit for about 15 minutes (the color will take awhile to process--it's best to let it sit rather than adding more and more right away). Add more color if necessary, until desired black tint is achieved.
If you are using a stand mixer or handheld mixer:
  1. In a bowl of stand mixer fitted with paddle attachment, or with a handheld mixer, beat the butter on medium speed until pale and fluffy, about 6 minutes. Sift together the confectioners' sugar and cocoa powder. Reduce to speed to low, and add the confectioners' sugar, cocoa powder, water, sour cream, vanilla, and salt and beat until incorporated, about 1 minute. Increase the speed to medium and beat for 2 more minutes. Add the melted chocolate and beat on medium speed until smooth, about 1 minute. Add a small amount of the black color (about 1 teaspoon). Pulse until combined. Let sit for about 15 minutes (the color will take awhile to process--it's best to let it sit rather than adding more and more right away). Add more color if necessary, until desired black tint is achieved--remember that it continues to darken over time.
Assembly of the Glam Rock Layer Cake:
  1. Put your first cake layer top-up on an 7" round cake board or 9" plate, and spread one-third of the purple frosting on top. Repeat with all of the layers, placing the final cake layer top-down. Make sure that your layers are straight and lined up with the ones below. Wrap the cake in plastic wrap and chill for at least 15 minutes.
  2. Remove the cake from the fridge and, using a turntable, if possible, frost entire outside of cake with a thin layer of the black frosting to seal in the crumbs. Chill until the frosting begins to firm-up, about 30 minutes.
  3. Remove the cake from the fridge and return it to the turntable. Cover the cake with a thick, even and smooth layer of the black frosting using an offset spatula, reserving about 1 1/2 cups of frosting for the piped top border. Return the cake to the fridge and chill for another 20-30 minutes.
  4. You will want the frosting for the buttercream "poof" border to be very soft, in order to achieve the appealing peaks. Warm frosting in a small heatproof bowl for about 8-10 seconds, and stir. Fill a pastry bag fitted with a large plain round tip with the softened frosting and pipe some buttercream "poofs" around the top perimeter of the cake.
  5. Pour your sprinkles into a medium bowl and gently press sprinkles onto the bottom third of the cake, all the way around, letting the excess fall back into the bowl. You can also put the cake on a cookie sheet and let the excess sprinkles fall onto the sheet. Return the cake to the fridge until the buttercream poofs are very firm, about 30 minutes. Pour more sprinkles atop the flat exposed surface of the top of the cake. Cake will keep covered at room temperature for up to 3 days. Serve at room temperature.