For the cake
4 eggs
100 grams of sugar
120 ml milk
120 ml vegetable oil
100 grams of flour
2 teaspoons baking powder
30 grams of cocoa powder
200 ml of blueberry juice
For the mousse filling
400 grams blueberries
500 ml double cream
100 grams of sugar
2 egg yolks
2 teaspoons of powdered gelatin
1 satchel of whipping cream stabilizer
For the cake, separate the yolks from the whites and beat the egg whites until stiff peaks form, then add the sugar and whip some more, to incorporate. Add egg yolks, one at a time and whip briefly. Sift the flour, cocoa, the baking powder twice, and it to the egg batter, alternating with milk and oil. Pour the batter into two prepared pans (8") and bake, in a preheated oven, at 190°C. Do the toothpick test to check for doneness. Remove from pans and set aside to cool completely.
For the mousse, puree blueberries in a blender, sprinkle with half of the sugar and cook over low heat until it thickens. Soak gelatin in a little water and leave it to activate. Remove the blueberries from the heat, and stir in the activated gelatin. Set it aside to cool. Beat the egg yolks with the second half of sugar in a double boiler, to get a thick cream. Whip the whipping cream (with the addition of the whipping cream stabilizer) until stiff peaks form, then combine with a cooled egg and sugar mixture. Then, gently fold this in into the cooled blueberries.
To assemble, put the first cake layer on the bottom of a spring-form pan, then soak it with half of the blueberry juice. Spread the mousse evenly and put the other cake layer (soaked with blueberry juice as well) on top of that. Leave the cake in the fridge overnight to cool down and firm up, then decorate as desired and serve.
