Rhubarb panna cotta cake

➊ For the sponge cake , thoroughly mix all the dry ingredients. Quickly stir the mineral water, rapeseed oil, lemon zest, and vanilla seeds into the flour mixture. Spread the batter thinly onto a baking sheet lined with baking paper and bake immediately at 180°C for approximately 20–22 minutes.

➋ To make the rhubarb compote , cut off the base and end of the rhubarb, then dice all but one of the stalks and set aside. Finely dice the remaining stalk to use as the compote filling. Pour the rhubarb juice into a saucepan and cook with the rhubarb pieces until soft, then puree finely. Bring the purée to a boil with the lemon juice and zest and the vanilla seeds and sweeten with sugar to taste. Add the agar agar, let it swell and simmer for another 2-3 minutes. Now add the finely chopped rhubarb cubes and bring to a boil briefly. Allow to cool slightly, then add the raspberry puree and the grenadine syrup and stir. Transfer the compote to a shallow dish and chill until it begins to thicken. Before using it for another time, stir briefly with a spatula until it is creamy.

➌ For the vanilla panna cotta , pour the cream into a saucepan, split the vanilla pods lengthwise, and add them to the cream. Bring to a boil briefly and let it steep for 20 minutes. Then remove the pods from the cream and scrape out the seeds. Return the vanilla seeds and lemon zest to the cream. Mix the sugar with the agar-agar to prevent clumping and add it to the cream. Bring the mixture to a boil, stirring constantly, simmer for one minute, and then let it cool until it begins to thicken.

➍ To make the rice paper air cushion, place the rice paper in water and place a second sheet on top. Smooth out any air bubbles between the sheets. Cut into 6 x 6 cm squares using a pizza cutter or sharp knife. Place on a rack lined with baking paper. Bake in a preheated oven at 180°C (convection oven) for 4 minutes, until they rise. Burn a hole in the cushion with a hot needle. Then fill the air cushions with fruit puree or fruit gel.

➎ For the apple gel, peel two apples and remove the cores, then dice them. Cook them with the juice, vanilla pod, and a little sugar until soft. Then blend until finely chopped using a hand blender and refine with a dash of Calvados. Add the agar-agar and let it swell for 5 minutes, then bring the compote to a boil. Transfer it to a shallow dish and leave to cool completely in the refrigerator until firm. Peel another apple, cut it into small, even-sized cubes (brunoise), and fry it in a pan without any fat until soft. Allow to cool and set aside. Using a hand blender, finely chop the gelled apples. Combine the fried apples with the apple gel and transfer to a piping bag. Refrigerate for later use.

➏ For the raspberry gel, combine the raspberry puree, lemon juice, sugar, and agar agar and let it swell for 5 minutes. Bring to a boil briefly, then pour into a shallow dish and refrigerate to set. Cut the jelly into large cubes and place in a blender. Blend until smooth. Transfer the gel to a squeeze bottle or piping bag. Set aside until ready to use.

➐ For the rhubarb gel, dice the rhubarb into large cubes. Place the rhubarb juice and cubes in a saucepan with the cinnamon stick and sugar and simmer until the rhubarb is soft. Then remove the cinnamon stick from the pan. Blend everything finely with a hand blender and pass through a sieve. Add the agar agar to the rhubarb puree and let it swell for 5 minutes. Then simmer for 3-4 minutes, then transfer to a shallow dish and refrigerate to set. Cut the rhubarb jelly into large cubes and blend finely in a blender. Transfer to a piping bag and set aside.

➑ Mix the ingredients for the aquafaba and divide them between the two sponge cake decorations.

➒ For the light-colored decorative sponge cake, cream the butter and powdered sugar until light and fluffy. Beat the aquafaba until stiff peaks. Stir the flour and aquafaba alternately into the butter mixture. For the red decorative sponge cake, cream the butter and powdered sugar until light and fluffy, then beat the aquafaba until stiff peaks. Stir the flour and aquafaba alternately into the butter mixture. Color the dough with food coloring as desired. Spread the red sponge cake mixture onto a baking mat fitted with a decorating stencil or a serrated comb and freeze. After about 30 minutes, remove the frozen decoration and immediately spread a wafer-thin layer of the light-colored sponge cake mixture on top. Bake at 200°C for 3–5 minutes until dry but soft.