After adding the melted chocolate you can flavor the brownie dough with cinnamon, ginger or tonka beans.
Hazelnuts can be substituted for other roasted nuts such as almonds, walnuts, pecans or peanuts!
For an even more intense flavor you can use 65-70% dark chocolate.
Try replacing some of the butter (up to 50%) with coconut oil for a fruitier aroma!