How to cook
Make the 1st layer by beating the eggs with the vanilla and sugar to a creamy mixture in a bowl. Sift the flour with the baking powder and add them to the egg mixture. stirring with a wooden spoon until homogeneous.
Put baking paper in a large, flat, rectangular oven dish, smear it with a little oil and pour in the mixture. Spread it along the entire surface of the oven dish. Put it in a preheated 356°F (180 °C) oven for about 20 min. until a toothpick comes out try when you poke it. Take the layer out and leave it to cool.
Make the 2nd layer the same way as the first but add cocoa this time to color it. Put it in the same oven dish with baking paper and once ready, remove it from the oven dish and leave it to cool.
Make the cream as instructed on the packet.
Invert one of the layers, carefully remove the baking paper and divide it in 2 to obtain 2 rectangles. Do the same for the other layer.
Assemble the cake: put 1/2 of the white layer in a platter, syrup it with a little milk, smear with the jam, pour in part of the cream, cover with half the cocoa layer. Next, syrup it, smear with jam, cream, cover with the white layer and continue you've placed the last cocoa layer. Smear it with jam and generously with the remaining cream.
Decorate with blackberries and leave the cake in the fridge for a few hours.