Melt the chocolate in the cream and chill it at least 2 hours in the fridge

Melt the butter with the cocoa in the milk. Wait until it cooled down a bit and add the eggs. Mix.

Add the sugar and the vanilla sugar and mix it.

Mix the flour, the baking soda and the baking powder in a differential bowl. Add it to the rest and mix it.

Put the dough into a spring-form pan and bake it at 380℉/170℃ for 35 until 45 minutes (test it after 35 minutes).

Let it cool down and cut it carefully into 3 parts.

Melt the nutella in a doubleboiler.

Take the liquid chocolate cream from the fridge, add the 'whip it' and whip it until it is stiff.

Take 1/3 from the stiff cream and put it on the first base. Put the second base on it.

Spread the nutella and afterwords 2/3 of the chopped hazelnuts on the second base. Put the third base on it.

Spread the rest of the cream on the whole tart and decorate it with the rest of the chopped hazelnuts and the 'ferrero Rocher's

Chill the tart at least 1 hour in the fridge.