Hibiscus Kombucha Cake
Few years ago I made tiramisu, but instead of dipping the ladyfingers in espresso, I dipped them in coffee kombucha, and instead of using cocoa powder, I roasted and ground linden fruits. It was a glorious success. In a similar fit of inspiration a few months ago, I had a vision of a hibiscus kombucha cake! The idea was to use the hibiscus kombucha in two ways, to dip the ladyfingers in (instead of the espresso), and to reduce the kombucha to a syrup to be mixed with the mascarpone filling. All topped with some raspberries and blackberries.
The category is — floral & fruity!
The recipe I developed was borne of twists on Alison Roman’s Tiramisu recipe & Rene Redzepi’s kombucha recipe.
Ingredients
For the Hibiscus Kombucha
300g dried hibiscus flowers
240g sugar
1800ml water
200g store-bought fruity kombucha
1 SCOBY
For the Hibiscus Kombucha Syrup
400ml hibiscus kombucha
50g sugar
For the Cream
4 egg yolks
100g sugar
3/4 cups heavy cream
For the Assembly
300ml hibiscus kombucha
24-30 ladyfingers
300g raspberries
200g blackberries
Process
Make the Hibiscus Kombucha
Boil about 800ml of water and mix in the 240g sugar until it is dissolved. Once dissolved, remove from fire and add the hibiscus flowers. Leave to seep for at least 10 minutes, or longer depending on how intense you want the hibiscus flavor and color (more is more in my book!).
In a 2 liter jar, strain the hibiscus tea, and add 1000ml cool water. Once the mixture is at room temperature, add the SCOBY and 200g kombucha (the kombucha helps kick start the fermentation). Cover with a breathable cloth and seal the it with a rubber band.
Leave the kombucha at room temperature for 7-10 days. The exact amount of time will depend on the temperature and your SCOBY, but start testing around day 7 to see if the kombucha is done to your liking. Once you reach the desired tartness, strain the kombucha and put your SCOBY in its new home (I usually use a 800g water+200g sugar+100g kombucha as a home if I don’t want to make another batch — see the Noma Fermentation guide for more tips!).
You can skip this step and buy 700ml of kombucha from the store — any pinkish/fruity flavor should do!
Make the Syrup
Mix 400ml kombucha and 50g sugar in a small pot. Set on medium-low heat until it starts to slowly evaporate. Reduce it to about half a cup, until it thickly coats the back of a spoon, which took me ~30 minutes — make sure you keep looking at the syrup while it evaporates, you don’t want to let it boil vigorously or over-reduce. Err on the side of too thick rather than too thin. Once done, make sure the syrup reaches room temperature before proceeding to the next step.
Make the mascarpone & hibiscus cream
In a medium bowl, beat 4 yolks and 50g of sugar with an electric mixer until pale mixture forms that leaves soft peaks, and is significantly increased in volume. Add the syrup and beat until the mixture is homogeneous.
Beat the heavy cream with 50g of sugar until the mixture leaves soft-to-medium peaks (you want it to get some density but not become too firm). Mix in the mascarpone cheese until the mixture homogeneous.
With a rubber spatula, mix in the mascarpone cream into the yolk and syrup cream, and gently fluff the mixture until it is homogeneous.
Assemble
Put 400mk kombucha in a flat bowl. Take a 9in round springform pan, and start making the ladyfingers layer. Quickly dip the ladyfingers in the kombucha, and layer them in the pan. The ladyfingers are super porous and this is where the aesthetic-texture trade offs kick in: let them soak longer, get a prettier purple cake, but also a soggier cake! Break the soaked ladyfingers to make sure they fit the cake, though it is ok if small spaces remain here and there. Spread half of the cream on top of the layer of ladyfingers, making sure you fill in any gaps well and that you spread the cream all the way to the edges.
Repeat: make another layer with the remaining ladyfingers, and spread the remaining cream on top. Are you paying attention children: that is ladyfingers-cream-ladyfingers-cream! Make sure the top cream layer is flat.
Top the cake with the raspberries and blackberries however you want, this is your journey. Let the cake chill overnight in the fridge to help it firm up.
Serve & eat
When ready to serve, remove the pan’s band, slice, and enjoy!
