Combine the chocolate mixture and butter in a bowl, melt in the microwave (in 20-second bursts) until completely melted and smooth, then cool slightly.
Incorporate the sugar, then add the eggs one by one, mixing well after each one.
Add the flour and 2/3 of the previously chopped hazelnuts, mix and transfer to a 28 cm diameter pan, previously lined with parchment paper.
Cover with the remaining hazelnuts as desired and bake for 35-45 minutes at 170°C.
The cake can be enjoyed both warm and cold, served with ice cream if desired.
Enjoy!
