Preheat the oven at 175 degrees Celsius.
Divide the chocolate in pieces.
Stir together the sugar and the eggs. Don´t use an electrical mixer that make the cake fluffy.
Melt the butter in a saucepan, add the chocolate and stir until melted.
Add the chocolate mixture and the salt in the sugar mixture and mix.
Add the vanilla sugar, cacao powder and the flour and stir together.
Place a baking paper in a baking form. Pour the batter in the form and place in the middle of the oven for approx. 25 minutes.
Make sure the cake is still sticky in the middle when you take it out.
Let the cake cool down in room temperature before serving it together with whip cream.