Start by chopping and roasting your hazelnuts for 10 minutes on 180C.
In a glass bowl add butter and dark chocolate and melt on low in a microwave.Once melted mix in the salt and vanilla extract and sat aside.
In a mixing bowl add the caster sugar and eggs and mix on high-speed for 3 to 5 minutes until the mixture is light and fluffy.
While mixing start adding the hot melted chocolate slowly to avoid cooking the eggs. Once you poured in all the chocolate mix in on a medium speed for 3 minutes.
Sift in the flour and fold until everything is mixed through.
In a baking tray add the toasted hazelnuts followed by the brownie. Bake for 30 minutes on 160C.
Leave the brownie to cool down for few hourse before slicing and serving.