This cake is just so impressive and fun when you slice into it. The combination of tart lemon and sweet, dark berries coupled with the rich buttercream frosting make this a refreshing yet decadent dessert.
Technique tip: Use a small angled palette knife to smooth out the batter before baking and to spread the icing. These work really well for getting an even layer.
For the butter cream, the butter should be softened, but not warm. This makes for a better consistency. The buttercream can be made up to 3 days in advance and stored in the fridge or freezer. Just bring it back to room temperature and quickly whip it in the electric mixer to restore its fluffiness before spreading.
Although the cake is best eaten on the day it's made, any leftovers will be fine the following day if stored in the fridge. As always, bring it back to room temperature before serving.
Swap option: Blackcurrents are not always easy to get hold of. Blackberries (or frozen mixed berries) will work just was well to get the bright color.
For the cake:1.
Preheat the oven to 400°F. Line a shallow 12- by 15-inch rimmed baking sheet with parchment paper and set aside.2.
Place the egg yolks in the bowl of an electric mixer with the whisk attachment in place. Add the 2/3 cup plus 2 tablespoons granulated sugar and the lemon juice and beat on medium-high speed for about 3 minutes, until pale and thick. Transfer the mixture to a large mixing bowl and sift the flour and salt directly over the egg mixture in two batches, folding through the mixture with a rubber spatula after each addition. Sprinkle the lemon zest on top and set aside.3.
Place the egg whites in a clean bowl of an electric mixer with the whisk attachment in place. Whisk on medium-high speed until soft peaks form, then slowly pour in the 1½ tablespoons granulated sugar. Continue to whisk until firm peaks form, then gently fold a third of the egg whites into the egg yolk mixture until incorporated. Finally, fold in the remaining egg whites until combined, and then scrape the mixture into the lined baking sheet. Even the surface out with a small spatula and bake for 15 minutes, or until light golden brown and a toothpick inserted into the center comes out clean.4.
Remove from the oven and place on a wire rack to cool in the pan for 5 minutes before dusting the top lightly with powdered sugar. Place a clean kitchen towel on top of the sponge cake and then flip it over so that it is now lying on top of the kitchen towel. Carefully peel away the paper and trim the very edges of the sponge. Be careful not to cut away too much, you really just want to straighten out the edges. Starting at the shorter edge of the cake, carefully roll it up (along with the kitchen towel). This is to "train" the cake, ready for rolling up again later. After about 20 minutes, or when no longer warm, unroll the cake. With the short end facing you, measure and cut three equal strips parallel to the long edge, each about 4 inches wide. (If you have a pizza cutter, this is a really easy way to cut the strips.) Cover with a clean kitchen towel and set aside.
For the purée:
Place 10½ ounces of the black currants and granulated sugar in a medium saucepan and place over medium-low heat. Warm through for 4-5 minutes, until the blackcurrants (or berries) have softened and the sugar has dissolved.
Transfer to a food processor and process to form a purée. Strain through a fine-mesh sieve set over a bowl to catch the purée; you only need 2/3 cup, so save any extra in the fridge for another use.
For the buttercream:1.
Place the corn syrup, granulated sugar and vanilla seeds in a medium saucepan. Place over low heat and stir until all the sugar dissolves; this is your sugar syrup.2.
While the syrup is cooking, place the egg yolks in the bowl of an electric mixer with the whisk attachment in place. Beat on medium-high speed until thick and pale yellow in color. Leave the machine on while you check the sugar syrup; when all the sugar has melted, stir again, increase the heat to medium and simmer until bubbles begin to appear. Swirl the pan gently and continue to simmer until there are large bubbles all over the surface of the syrup.3.
Remove the pan from the heat and carefully pour the hot syrup in a slow, steady stream down the edge of the mixing bowl into the beating yolks. When all the syrup has been added, increase the mixer speed to high and continue to beat the mixture for about 10 minutes, until the outside of the bowl is no longer warm. Gradually add the butter, one cube at a time, allowing it to be incorporated into the mixture before adding the next. When all the butter has been added, scrape down the bowl and continue to beat for another minute, until the buttercream is very smooth and light. Add a scant 1/2 cup of the blackcurrant purée and beat on medium speed until fully incorporated.
Spread each of the strips of sponge with about 3 ounces of the buttercream; this should leave about 10½ ounces to frost the top and sides of the cake. Take one strip of sponge and, starting with the short end, roll it up. Once this strip is rolled, position the exposed end at the beginning of the next strip and keep rolling. Again, once this is rolled — the cylinder will be getting wider now — position the exposed end at the beginning of the last strip and continue to roll. You now have a rolled cylindrical cake! (Imagine, for a moment, if you lined up the three strips end to end to create one very long strip. Then imagine rolling that very long strip up, from one end to the other. You should end up with a coiled barrel shape.) Turn the cylinder onto the serving plate so that it is standing on one of its flat ends.
Spread the remaining buttercream all over the top and sides of the cake, smoothing with a spatula to create an even surface. Dribble the remaining 1/4 cup blackcurrant purée on top of the cake and top this with the remaining blackcurrants. Set aside for 1 hour at room temperature (or in the fridge if it is a very warm day) before serving.
Reprinted with permission from Sweet: Desserts from London's Ottolenghi by Yotam Ottolenghi and Helen Goh, copyright © 2017. Published by Ten Speed Press, an imprint of Penguin Random House LLC.