- For the ganache filling and frosting:
- 1 1⁄3 cups heavy cream
- 14 ounces bittersweet chocolate, finely chopped
- 2 1⁄2 tablespoons Grand Marnier
- For the cake layers:
- 18 ounces bittersweet chocolate, melted and still warm
- 2 tablespoons light corn syrup
- 10 large egg yolks
- 1⁄2 cup plus 2 tablespoons unsalted butter, softened
- 3⁄4 cup almond flour*
- Scant 1⁄4 cup dark rum (optional)
- 10 large egg whites
- 3⁄4 cup granulated sugar
- *Almond flour is a mixture of finely ground almonds and sugar, available in specialty gourmet stores and health food stores. If you can't find almond flour, use an equal amount of finely ground walnuts or pecans instead.
To prepare the truffle ganache: Heat the heavy cream in a 2-quart heavy-bottomed saucepan until bubbles begin to form around the edge of the pan. Place the chopped chocolate in a medium-sized mixing bowl. Pour about half of the hot cream over the chocolate and let it sit for 30 seconds to melt the chocolate. Then slowly whisk until smooth. Add the remaining cream gradually and mix until all of the hot cream is incorporated and the ganache is smooth and consistent. Pour the ganache onto a baking sheet lined with parchment paper to cool. When the ganache has cooled to the consistency of toothpaste but is still easily spreadable, it is ready to be used. If the ganache has cooled too much, you can soften it by heating a small amount in a saucepan placed over medium heat until melted. Then, quickly but gently stir the melted ganache into the harder, cooler ganache. If the ganache is still too hard, repeat the procedure until the desired consistency is reached.
To make the cake layers: Preheat the oven to 325F. Combine the corn syrup, egg yolks, butter and almond flour in a medium-size mixing bowl and beat with an electric mixer set on medium speed until well incorporated, light and fluffy.
Place the egg whites in a large mixing bowl and whip until foamy, using an electric mixer set on medium speed. Gradually add the sugar, 1 tablespoon at a time. Increase the mixer speed to medium-high and whip until stiff but short of forming dry peaks, about 7 minutes. The meringue should be stiff but not overwhipped and separated, or it will collapse when combined with the warm chocolate. Fold the meringue into the creamed butter mixture all at once. Fold up from the bottom of the bowl and fold carefully so you do not deflate the meringue. When the two mixtures are almost fully incorporated, add the warm chocolate. Use a rubber spatula and be sure to fold up from the bottom of the bowl. If you have some meringue that does not want to incorporate, carefully and gently break it apart by folding, not whisking, with a whisk.
Pour the batter onto a baking sheet lined with parchment paper and spread it evenly with a rubber spatula. Carefully push the batter. Do not smash it or you will lose the incorporated air and the cake will be flat and chewy. Place the cake in the oven and bake until the cake springs back when gently pressed, about 35 minutes. You can also test the cake with a wooden toothpick. Insert it into the center of the cake; if it comes out clean, the cake is done. Remove from the oven and place the baking sheet on a wire rack to allow the cake to cool. The cake will rise in the oven and then collapse slightly as it cools.
When completely cooled, remove the cake from the baking sheet by running a sharp paring knife around the sides of the cake. Invert the cake onto a clean work surface or sheet of parchment paper and remove the paper clinging to the back of the cake. Use a sharp chef’s knife to cut the cake into four equal-sized squares. You will only use three squares for this cake. Store the fourth square in the freezer. Trim each square to make clean edges. If the cake is too delicate to move, cut the cake into four pieces while it is still on the baking sheet. Place the baking sheet in the freezer until the cake layers are cold enough to move without breaking.
To assemble the cake: Slide one square onto a cardboard cake circle or flat platter. I like to anchor the cake layer by first placing a small dab of ganache in the center of the cake circle. Use an offset spatula to spread about a 1Â¼2-inch-thick layer of ganache onto the cake square. Be sure to spread the ganache all the way to the edges. Top with a second cake layer, making sure the second layer rests evenly on the first. Repeat with the ganache. Top with the last cake layer and press down slightly to adhere. Use a large offset spatula to spread an even layer of ganache over the top and sides of the cake. If the cake is uneven, use the ganache frosting to make it as flat and even as possible. At this point you can place the cake in the refrigerator until the ganache has hardened, about 20 minutes. Then use the offset spatula to make the edges as clean and straight as possible. Place the frosted cake in the refrigerator for about 1 hour to set before decorating.
Remove the cake from the refrigerator and place it on a cake platter. Scrape the remaining ganache into a pastry bag fitted with a star tip. Using a spoon or spatula to transfer the ganache will help to ensure you don’t have lumps in the ganache. Lumps will clog the pastry tip and make it difficult to use. Pipe decorations around the side and top of the cake.
If you do not plan to serve the cake within a few hours of assembling it, store it in the refrigerator until ready to eat. If the cake has been stored in the refrigerator, allow it to come to room temperature for at least 30 minutes before serving. It is easiest to cut the cake with a hot chef’s knife. To heat the knife, dip it in a tall container filled with hot water before each cut and wipe off the excess water. If you like, you can serve this cake with some fresh berries.