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1
Preheat oven to 350u00b0F. For the cake, beat the egg whites with 3 tablespoons of cold water. Drizzle in 3/4 cup sugar, 1/2 tsp vanilla extract and a pinch of salt. Next, mix in the egg yolks one at a time. In a separate bowl, sift together the flour, 3 tbsp cornstarch and baking powder, then carefully fold dry ingredients into the wet. Finally, fold in the ground almonds.
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2
Line the bottom of a 10 inch springform pan with parchment, then spoon in the cake batter, smoothing the top with a flat knife. Bake for about 25 mins, then remove from the oven and allow to cool on a wire rack.
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3
To prepare the grapefruit segments, using a sharp knife, slit between the membranes of 4 grapefruits and lift out the skinless segments. Squeeze any remaining juice out of the grapefruit skins.
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4
Release the cake from the pan, set the cake on a work surface and clean the cake pan. Using a long, flat knife, cut the cake horizontally into 3 equal layers. Next, mix the grapefruit juice with the orange juice to make 1 1/4 cups. Take 2 tablespoons of the juice and blend it with the rest of the cornstarch in a bowl. Pour the rest of the juice into a saucepan, add a tablespoon of sugar and bring to a boil, then briskly stir in the cornstarch slurry and cook until thickened. Take the pan off the heat and stir in the grapefruit segments. Place the bottom layer of the cake back in the clean cake pan, then spread grapefruit compote on top of bottom layer. Refrigerate the cake for 15 mins.
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5
For the white chocolate mousse, soak the gelatin in a few tablespoons of cold water. Meanwhile, melt the chocolate in a bain marie or a heat-proof bowl over a pan of hot water. Next, in a small saucepan, heat 1/4 cup of the cream with a tablespoon of sugar. Add the bloomed gelatin to the pan (if using gelatin leaves, squeeze out the excess moisture first); stir until the gelatin has dissolved, then remove from heat and stir into the melted chocolate. In a separate bowl, whisk 1 cup of the whipping cream until it is stiff, then fold into the chocolate sauce.
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6
Place the second layer of cake onto the bottom layer. Spread the white chocolate mousse over the second cake layer and then carefully place the third layer on top. Refrigerate for 2 hours. Meanwhile, toast the almonds in a dry skillet until they are golden brown, then remove and allow to cool.
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7
To decorate the cake, whisk the rest of the cream with a half-teaspoon of vanilla extract and 2 teaspoons of sugar. Next, release the cake from the pan and transfer to a serving plate. Cover the top and sides of the cake with the whipped cream, then decorate with some toasted almonds around the sides. Cut the remaining 4 grapefruits into thin discs, arrange on top of the cake and serve.
