Preheat the oven at 175 degrees Celsius.
Place a baking paper on a baking sheet.
In a bowl mix the flour, baking powder, cacao powder and salt together.
Separate the egg yellows and the egg whites in two different bowls.
With an electrical mixer whisk the egg yellows together with the sugar.
Melt the butter and add in the egg yellow mixture.
Add creme fraiche and vanilla sugar and mix well.
With an electrical mixer whip the egg whites to a hard foam.
Add 1/3 of the egg white foam to the batter and fold gently in the batter.
Add the rest of the egg white foam and fold gently together until well combined.
Spread evenly on the baking paper.
Place in the middle of the oven for 10 minutes.
Take out the cake and transfer the paper on to the counter.
Make a roll by folding the cake from the short end, with the paper still on.
Time to make the filling. In a big bowl whip the cream together with the vanilla sugar icing sugar and salt.
Add the mascarpone cheese and continue whipping until stiff peaks forms.
Unroll the cake bottom and spread evenly the filling on it.
Reroll gently (without the paper) the cake together again.
Cover with plastic foil and place cold for minimum 1 hour.
Time to make the topping. Break the chocolate in pieces and place in a bowl.
Heat up the heavy cream and pour over the chocolate. Do not mix together.
Stir the cream and chocolate together and let it become room temperature.
Whip together to a foam by using an electrical mixer.
Take away the plastic foil from the cake and place on the plate you want to serve the cake on.
Cut away a piece from one of the edges, and place it one of the sides of the cake.
Spread evenly the topping all over the cake.
With a fork make lines from one side to the other all over the cake.
Time to decorate the cake.
Place cold until it's time to serve.