Separate eggs. Beat the egg whites and 3 tablespoons of cold water with the whisk of the hand mixer until stiff, adding sugar, 1 packet of vanilla sugar and salt. Beat the egg yolks one after the other. Mix flour, 3 tbsp. starch and baking powder, sieve onto the egg yolks. Carefully fold in ground almonds
Line the bottom of a springform pan (26 cm Ø) with baking paper. Fill in sponge cake mixture and smooth it down. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 25 minutes. Leave to cool in the mould on a cake rack for approx. 2 hours
Peel the grapefruit so that the white skin is completely removed. For 4 grapefruits, remove the fillets with a sharp knife between the parting skins. Press the juice out of the parting skins
Remove the sponge cake base from the mould, cut through horizontally twice and place a cake ring around the lower base. Pour grapefruit juice with orange juice to 300 ml. Remove 2 tbsp. juice and mix with 25 g starch. Bring the rest of the juice and 1 tbsp. sugar to the boil and thicken with the starch. Remove from the heat and stir in grapefruit fillets. Spread the compote on the lower cake layer and place the 2nd layer on top. Chill the cake for about 15 minutes
Soak gelatine in cold water. Finely chop the chocolate and melt over a warm water bath. Heat 50 g cream and 1 tbsp. sugar, squeeze gelatine well and dissolve in the cream. Gradually stir the cream into the chocolate. Beat 250 g cream until stiff and fold into the chocolate
Spread the chocolate cream on the 2nd base. Place the sponge cake lid on top and press down lightly. Chill the cake for about 2 hours. Roast the flaked almonds in a pan without fat until golden brown, take them out and let them cool down
Whip 150 g cream until stiff, while pouring in 1 sachet of vanillin sugar. Remove the cake ring and spread the cake with cream. Decorate cake ring with almonds. Cut the remaining 4 grapefruits into thin slices and cover the cake with them
waiting time approx. 4 hours