BLACKOUT FOREST CAKE
A hybrid, of sorts. This interlaced cake contains all the best from that which I remember, and love—Black Forest and Brooklyn Blackout. It’s rich, but not sweet, and I never slice it too thick or take it too high. You can interrupt the intensity with fresh cherries, if in season, or preserved, if desired. I let the Kirsch do all my heavy lifting.
For the sponge
7 large (140 g) egg yolks, 2 cups (240 g) confectioners’ sugar (sifted and divided), 9 large (360 g) egg whites, 1 cup (85 g) Dutch processed cocoa powder, ¼ cup (32 g) cornstarch, 2 teaspoons instant coffee powder, ¼ teaspoon salt
For the soak
1/3 cup (80 ml) Kirsch
For the buttercream
1 cup (200 g) granulated sugar, ¼ cup (60 ml) water, 6 large (120 g) egg yolks, 1 ½ cups + 1 teaspoon (350 g) unsalted butter (soft at room temperature), 2 tablespoons instant coffee powder mixed with 3 tablespoons of hot water (into a paste)
For the ganache
1 2/3 cup (280 g) dark chocolate (finely chopped), 1 ½ cups (360 ml) heavy cream
Adjust a rack to the middle of the oven, then pre-heat it to 200ºC (400ºF). Grease an 18 x 13 x 1 ¼-inch (45 x 33 x 3-cm) rimmed half sheet pan, and then line it with non-stick parchment paper, leaving a slight collar up the long sides. Lightly grease the paper, too.
In the bowl of a stand mixer that’s fitted with the whisk attachment, whisk the yolks with 1 cup (120 g) of confectioners’ sugar on medium-high speed until pale, thick, and voluminous, about 3 to 5 minutes. Set aside. Next, in a separate bowl, whisk the whites on medium speed until soft and foamy. Add in the remaining sugar, a tablespoon at a time, until it’s all used up. Continue to whisk until the meringue holds in glossy-thick peaks. Fold a third into the bowl with the yolks, followed by another third until almost combined, and then the last. Sift over the cocoa, cornstarch, coffee, and salt. Fold, tenderly, until just combined. Scrape the batter into the prepared pan, smoothing it out to the edges with an offset palette knife.
Bake for 25 to 30 minutes, until the sponge springs back when lightly pressed, and has started to pull away at the sides. Transfer to a wire rack, and leave to cool completely. Once cool, cut out three rounds using a 5-inch (15-cm) stainless steel cake ring as a guide. Gather the sponge scraps, reserving them aside in a bowl. Soak each round generously with Kirsch. Wrap tight.
Next, pre-heat the oven to 180ºC (350ºF). Line a large baking sheet with non-stick parchment paper. Crumble over the sponge scraps, scattering them into an even layer. Bake until dry, but not darkened to a crisp, 5 to 7 more minutes. Remove and cool, then blitz to a textured crumb in a food processor. Seal in an airtight container, and set aside for assembly.
For the buttercream, put the sugar and water into a medium saucepan. Bring to a boil over medium-high heat, swirling occasionally to help dissolve the granules. Continue to cook until the syrup reaches 250ºF (121ºC). Meanwhile, start whisking the yolks in the bowl of a stand mixer that’s set on medium-high speed. As soon as the syrup has reached temperature, stream it into the yolks between the whisk and side of the bowl. Raise the speed to high. Continue to whisk until thick and glossy, like velvet. All of the steam should have escaped, and the bowl no longer hot to the touch. Switch out the whisk for the paddle attachment. Beat in the butter, a tablespoon at a time, waiting until fully blended before adding in the next spoonful. Beat in the coffee paste. Continue to beat the buttercream for a few more minutes, until silky-smooth. Use soon after making.
To assemble, position a sponge round onto a plate, or preferably, a cake board. Spread over a few tablespoons of buttercream, smoothing it out with an offset palette knife. Add the second sponge. Again, spread with buttercream, then top with the last sponge, using light pressure to adhere. Cover the cake with the remaining buttercream, to smooth, patch, and fill. Transfer to the refrigerator, and chill for half an hour or so, until firmed. Meanwhile, make the ganache.
Put the chocolate pieces into a heatproof bowl, and pour the cream into a saucepan. Bring to a simmer over medium heat, then stream the liquid all over the chocolate. Stand for a minute to acclimatize, then stir until smooth. The ganache can’t be applied to the cake hot, so cool it on the kitchen counter, stirring occasionally, until thick but pourable—usually the time it takes for the buttercream to firm in the refrigerator.
To glaze, transfer the cake to a wire rack that’s set over a rimmed baking sheet. Pour the ganache over the top, and in one swift movement, slick it out with a large palette knife so that it drips down to coat the sides. Fill any gaps with residual ganache. Stand until adhered, then gently pat on the crumbs to cover. It’ll be messy and sticky, but delicious—all part of it. Chill again until set.
Serve the cake, slices cut with a warm knife. It’s best eaten on the day of making, but will keep loosely covered in the refrigerator for up to 3 days.
