Twelve layers of chocolate cake filled with alternating layers of silky chocolate pastry cream and rich fudgy chocolate frosting. This 6-inch tall mega cake might just be the best chocolate cake you’ll ever taste.
For the Chocolate Cake:
4 cups (500 grams) All-purpose flour
4 cups (800 grams) granulated sugar
2 cups (170 grams) unsweetened cocoa powder
4 teaspoons baking soda
2 teaspoons baking powder
2 teaspoons salt
5 large eggs, at room temperature
2 cups (452 grams) sour cream or Greek yogurt, at room temperature
2⅔ cup water, at room temperature
⅔ cup neutral-tasting oil
4 teaspoons vanilla extract
For the Simple Syrup Soak:
½ cup (100 grams) granulated sugar
½ cup water
For the Chocolate Pastry Cream: (makes about 4 cups)
2¼ cup whole milk
¾ cup heavy whipping cream
½ cup plus 3 tablespoons (137 grams) granulated sugar, divided
⅛ teaspoon salt
6 large egg yolks (freeze the whites for later use)
¼ cup (32 grams) cornstarch
¼ cup (57 grams) cold unsalted butter, cut into 4 pieces
4 ounces/ 114 grams finely chopped bittersweet chocolate (I used 66% dark chocolate callets)
1 teaspoon pure vanilla extract or 2 teaspoons imitation vanilla flavoring
For the Fudgy Frosting: (makes about 4 cups)
12½ ounces/ 354 grams bittersweet or semisweet chocolate or a combination of both (I used ½ bittersweet, ½ semisweet)
1¼ cups heavy whipping cream
1¼ cups (250 grams) granulated sugar
Heaping ¼ teaspoon salt
½ cup plus 2 tablespoons (142 grams) unsalted butter, softened to room temperature
For Garnish: (Optional)
Chocolate sprinkles, colored sprinkles, chocolate chips or chocolate curls/shavings (I used these chocolate flakes)
For the Chocolate Cake: (Can be prepared several days in advance)
1. Adjust oven rack to middle position and preheat the oven to 350F/180C. Spray (or grease) four 9-inch round cake pans with non-stick cooking spray, line with parchment paper, then spray (or grease and flour) the parchment and pans. If you don’t have four 9-inch pans, use whatever amount you have and bake in intervals. You just want to end up with four equal cake layers.
2. In a very large bowl, sift together the flour, sugar, cocoa powder. baking soda, baking powder and salt.
To the dry ingredients, add the eggs, sour cream, water, oil, vanilla extract and mix together using an electric mixer until well combined and smooth. Batter will be very thin.
3. Divide the batter evenly among the prepared pans. A great way to do that, is to weigh the batter, and divide that number by the amount of pans used, which is 4 in the case of this recipe. Using a scale to measure, fill each pan with the resulted amount.
4. Bake until the center of the cakes spring back when pressed lightly with your fingers and a toothpick inserted into the center of each cake comes out clean (a few moist crumbs attached are ok); about 25 minutes.
5. Let the cakes cool in the pans on wire rack for 15 minutes. Invert cakes onto a cake board or plate and peel off parchment; reinvert cakes onto the wire rack. Allow to cool until slightly warm or at room temperature, then wrap in a double layer of plastic wrap and keep in the freezer until cold and firm but not frozen. This step is optional, but it makes the process of slicing the cakes into thin layers, cleaner and easier. Alternatively, you could keep the cakes in the freezer for up to several days,
Meanwhile, make the other cake components.
For the Simple Syrup Soak: (can be prepared up to a week in advance)
Combine the sugar and water in a small saucepan and heat over medium heat, stirring occasionally, until the sugar has dissolved; set aside to cool completely before using.
For the Chocolate Pastry Cream: (Can be prepared up to 2 days in advance)
1. Heat the milk, heavy whipping cream, ½ cup (100 grams) of the sugar, and the salt in a medium heavy-bottomed saucepan over medium heat until simmering, stirring occasionally to dissolve the sugar.
2. Meanwhile, whisk the egg yolks and the remaining 3 tablespoons (37 grams) of sugar in a medium bowl, until the sugar has begun to dissolve and the mixture is creamy, about 15 seconds. (IMPORTANT: Don’t whisk the egg yolks and sugar together until the milk mixture is already heating, because if left together for too long, the sugar will start to cook the yolks). Whisk in the cornstarch vigorously until the mixture is pale yellow and thick, about 30 seconds.
3. When the milk mixture reaches a full simmer, gradually whisk the simmering milk into the yolk mixture to temper. Don’t do it too fast, or you’ll risk cooking the eggs. Return the mixture to the saucepan, scraping the bowl with a rubber spatula. Return to a simmer over medium heat, whisking constantly, until a few bubbles burst on the surface and the mixture is thickened and glossy, about 30 seconds. Be careful not to cook the mixture beyond the point of a few bubbles or the mixture can start to curdle and the yolks may scramble…not fun! Turn off the heat, whisk in the butter, chocolate, and vanilla.
3. Strain the pastry cream through a fine-mesh sieve set over a medium bowl. Press plastic wrap directly on the surface to prevent a skin from forming and refrigerate until cold and set, at least 3 hours or up to 2 days.
For the Fudgy Frosting: (can be prepared 1 day in advance)
1. Place the chocolate in a large bowl.
2. Heat cream, sugar, and salt in saucepan over medium-low heat, stirring occasionally, until sugar dissolves and mixture begins to simmer. It is very important to make sure that the sugar has dissolved completely, so you don’t end up with a gritty frosting.
3. Pour hot cream mixture over chocolate and whisk until smooth. Whisk in the butter until glossy. Cover and refrigerate until icing is firm but still spreadable, about 1 hour.
To Assemble the Cake:
1. Since this mega cake is a 6-inch tall beast, it is best to treat it as 2 separate cakes that we’ll later fuse into one; it will make for a sturdier construction that way. Start by lining the bottom of a 9-inch cake ring or the ring of springform pan with a 9-inch round cake board. Line the inside of the ring with a strip of acetate or parchment paper. This will later help release the finished cake from the ring easily.
2. If your cakes are domed, level them off by slicing away a thin layer from the top; you need the cakes to be as flat as possible. Using a serrated knife or cake leveler, as careful as you can, slice each of the 4 cakes into 3 layers of equal thickness, about 1cm each. You should end up with a total of 12 layers.
3. Using a round cake board or cake lifter, transfer the bottom layer of one of the cakes inside the ring. Using a pastry brush, lightly brush the surface of the cake layer with the Simple Syrup Soak.
4. Using an offset spatula or back of a spoon, spread a little over ½ cup of the Chocolate Pastry Cream evenly over the cake layer, all the way to the sides of the ring.
5. Top with a second cake layer, then brush with the Simple Syrup Soak. Spread a little over ½ cup of the Fudgy Frosting evenly over the cake layer, all the way to the sides of the ring. Using up 2 of the 4 cakes, repeat, alternating layers of cake, Chocolate Pastry Cream, cake, Fudgy Frosting, brushing each cake layer with the Simple Syrup Soak. End with a smooth layer of Fudgy Frosting. You should now have 6 layers of cake and 6 layers of filling. Cover the cake loosely with plastic wrap and place in the freezer to set.
6. Using another 9-inch cake ring or the ring of springform pan, repeat Steps 3 through 5, using the remaining 2 cakes and the remaining Chocolate Pastry Cream, Fudgy Frosting and Simple Syrup Soak. Top the final layer of cake, decoratively, with the last bit of Fudgy Frosting creating swoops and swirls, as this will be the top layer of the final cake. If you don’t have an extra 9-inch cake ring (which I don’t) carefully slide the first cake out of the ring, keeping the acetate intact, cover, freeze, and reuse the same ring to assemble the other cake.
7. Freeze the 2 assembled base cakes until very firm and sturdy; 1 to 2 hours. You could even freeze it for several days (*For make ahead details, please refer to the NOTES below).
Pop the cakes out of the cake ring(s).
8. Gently peel off the acetate of the cake you plan to place on the bottom. Make sure the Fudgy Frosting topping on that cake, is soft enough to adhere to the top cake when placed on it. If its too cold and dry, warm through using a kitchen torch.
9. Top the bottom base cake with the top base cake (the one with the pretty swirls on top). Don’t forget to remove its cake board before you do! Peel off its acetate. Use an offset spatula to smooth out the sides of the cakes, fusing them together as you go, and scrapping off any excess and filling the gaps with it.
10. Place the final cake on a rimmed baking sheet to catch any decoration fall outs. Cover the sides of the cake with the garnish of your choice. I used these Chocolate Flakes.
11. Place the cake under a cake dome and allow to come to room temperature before serving. Timing will vary depending on how long the cake was left in the freezer. Serve at room temperature, or slightly warmed in the microwave. Leftovers will keep well chilled in the fridge in an airtight container.