How to cook
First, make the layer. Separate the egg yolks from the whites. You have to leave the yolks in the shells or other suitable containers, so that they remain separate. Beat the whites to hard snow, then gradually add the sugar spoon by spoon.
Add the yolks 1 by 1 as well, the goal is to beat the mixture very well. To make sure it all goes perfectly, you can add 2 tsp (10 g) baking powder to the flour. Gradually add the flour that's been sifted with the cocoa ahead of time into the egg mixture.
Pour the mixture into a greased form and bake about 40-45 min. in a preheated 392°F (200 °C) oven. Take it out, leave it to cool and divide it into 2-3 layers.
For the cream: Melt the liquid chocolate in a water bath with the butter and stir until you get a smooth mixture. In a separate container, melt 3.5 oz (100 g) of chocolate on low heat.
Add the sour cream and stir until you get a smooth cream, being careful not to let it come to a boil. Remove from the stove and add the sour cream, powdered sugar and cocoa and beat with a mixer. Add the hazelnuts whole and stir by hand.
For the syrup, heat the water, add the sugar and stir until completely dissolved. Syrup the first layer. Smear it subsequently with melted liquid chocolate, put 1/2 of the cream with hazelnuts on top.
Place the second layer and repeat this process. Place the third layer, syrup it, smear it with a thin layer of cream and pour melted milk chocolate over it. Use the remainder of the cream to smear the cake's sides.
Put it in the fridge for 4-5 hours and serve well cooled.