Preheat oven to 180 ° C.
In a bain-marie, mix the nutella with half the cocoa powder until you have a smooth mixture. Then add the walnuts or the filleted almonds.
Another vessel. Beat the eggs, then add the rest of the cocoa powder, the flour, and the sugar. To finish, add the chocolate from step 1. Mix all the ingredients well, it is important in this step to avoid lumps of flour.
Serve brownie mixture in baking dish.
Bake at 150 °C for 20 minutes. Remember the brownie should be slightly moist inside, but with solid crust.
Leave to cool for 3 hours.
Carefully unmold a board and cut into medium portions.