Sponge:

• Preheat the oven to 180 °C (356° F). Line a 20/30 cm (8x12 inches) baking tray with parchment paper and butter.
• Put the eggs, sugar, and pinch of salt in a mixer bowl. Mix until the eggs turn white and triple in volume (at least) – about 10 minutes. Gradually add in the oil and mix a little more.
• Separately, mix the flour and cocoa powder. Gently fold in the dry with the liquid ingredients, using upward motions.
• Pour the mixture into the baking tray and gently level it. Bake for 20-25 minutes, then remove to a metal cooling rack.

Blueberry mousse:

• Put the blueberries, water, sugar, and lemon juice in a small saucepan and bring them to a boil over medium heat. Leave to cook for 10 minutes, or until they soften. Put the mixture into the blender and purée it. Place back on the heat, bring to almost boiling point, then turn off the stove.
• Hydrate the gelatin in 3 tablespoons of cold water. After 5 minutes, incorporate into the blueberry purée. Let cool.
• Add two tablespoons of sugar to the yogurt and blend, then add it to the cooled blueberry purée and combine the two. Refrigerate the mixture until it gets a creamy consistency.
• Combine the whipping cream with the powdered sugar in a mixer, mixing until it becomes fluffy and aerated. Incorporate in the cream from the refrigerator with upward motions.

Raspberry mousse:

• Follow the same steps listed for the blueberry mousse.

Chocolate cream:

• Bring the milk to boiling point. Turn off the heat and add the broken chocolate pieces. After 2 minutes of rest, mix until fully combined.

Assembly:

• Put the sponge back into the baking tray. Spread the blueberry mousse on top and put the cake in the freezer for half an hour.
• Pour half the chocolate cream on top, level it, and return to the freezer for 10 minutes.
• Do the same with the raspberry mousse and the remaining chocolate cream. Leave the cake in the fridge for 2-3 hours to allow all the layers to set. Portion it up with a hot knife (keep the blade in hot water for a smooth cut).

Serve!