Preheat the oven to 180 °C (360 °F). Line a 20/30 cm (8 x12 inch) baking tray with parchment paper.
Melt the chocolate with the butter over a low heat. When the mixture is smooth, turn off the heat and let it cool. Then, incorporate the wheat flour and the almond flour into the chocolate mixture.
Whisk the eggs with the salt and sugar until they triple in volume and turn into a firm foam. Gently fold the eggs into the chocolate cream, using upward movements.
Pour the mixture into the baking tray and level it. Bake for 20-25 minutes until it passes the toothpick test. Transfer to a cooling rack.
When the cake is completely cooled, cut it into two pieces.
Chocolate cream:
Bring the whipping cream to a boil. Turn off the heat and add the broken chocolate pieces. Let it rest for two minutes, then stir well. Leave the cream to cool.
Blackberry mousse:
Hydrate the gelatin in cold water. Mix the blackberry jam with the water and boil it for 2-3 minutes. Turn off the heat and incorporate the drained gelatin.
Make the whipped cream by adding vanilla sugar to the whipping cream and mixing it at high intensity. Half of the mixture will be combined with the blackberry cream (cooled). The other half will be kept white and glossy.
Assembly:
Place one of the cake pieces back in the baking tray and spread the blackberry jam over it. Add the chocolate cream and then place the other cake piece on top. Alternate the two creams on top: blackberry and plain whipped cream.
Decorate the cake with chocolate, slice, and enjoy!